Photography is an expensive hobby. If it was your job, the cost of gear would actually pretty low. A camera cost far less than a restaurant ! But as a side activity, it can cost you an arm if you get carried on into a gear frenzy.
Luckily, a lot of people are totally obsessed by buying tons of gear, certain that they will get better photographers. That makes camera manufacturers very happy ! As a consequence, they do sell a lot of used equipment. As for many other things, Ebay will become your best friend :)
If you truly want to reach the heights of proper landscape / portrait photography, this is how much it costs.
Why should you buy used?
Obviously because it is much cheaper, but also because cameras, unlike computers, haven't fundamentally improved since the 80ies. In 1995, a Nikon F5 has faster AF, FPS and metering system than 99% of the actual DSLR production.
Of course marketer at Canon and Nikon will tell you the contrary, and no, I am not denying significant improvements occurred. You can shoot faster, more conveniently, in more extreme light conditions than ever before. However the question is: do you need any of that?
It is very likely that you don't.
For example, if you want to shoot landscapes, or artistic portraits, nothing justifies buying a brand new camera. Of course if you are rich, forget it. You can also stop reading this article :)
Shooting landscape of artistic portraits (with a posing model) non professionally can be done with an entry level DSLR and any tripod. It can be done marvelously with a film camera for much less money and better results too. Let it be very clear: a 400$ D3100 will do the same as a 5000$ D3 if you shoot with proper light and set your camera right. The same. The D3 is just faster, more resistant, more convenient; picture quality however won't be better if used properly.
If you shoot landscape in particular, you must - I insist you MUST - go for a larger format than 35mm (that is to say bigger than DSLR). A medium format camera, a really great one, will not cost you more than 1000$ all included on Ebay, when they still cost 3000-5000$ new ! Why? Because pros are selling their own for the convenience of digital, a convenience you don't need as an amateur. Also because it out performs 35mm cameras.
If you shoot wildlife or action, then yes, modern cameras are worth it. They perform faster, they can shoot well up to ISO 6400.
If you like making movies, a modern DSLR can be a great all in one tool for both. But how many of you actually shoot then edit movies?
If you back pack, maybe a more recent lighter camera is also a good idea.
If you are a pro of course, a state of the art camera can reduce your effort, make you more productive, but it's a totally different logic and need.
An other reason why to buy used: most of japanese or german gear is extremely durable. Nothing to do with you plastic XBOX 360. I own 30yo cameras that work as good as new, not one part moving or shacking. Consider it is like a very nice swiss watch. I personally apply that to everything: I bought my car like that, why paying full price when a as good as new model is 50% off with 30 000 miles? It can still go for 100 000 miles easy !
Last but not least, you won't targeted by thieves if your gear looks like it's already been stolen twice.
I shot these for the brand Zumo with a Nikon D80 & Nikon D700
, it was printed Xlarge on their shops here in Dublin although they are 10 -12MP cameras. My point: the used SLR you can get now for cheap was the pros' camera of 5 years ago ! If they were happy with it, why shouldn't you
What should you buy used?
Mostly camera bodies. First of all they are less risky to buy than a lens. Then buying a lens can be a 30 years investment worth the extra bucks, when a camera body will need to be replace long before the lens.
I however did buy used lenses, but not online. I could inspect them in the store, test them and return them in case I had a problem. If arguing with online sellers doesn't scare you, go for lenses as well but pay attention to where you buy !
Example of great products you can get used for much cheaper.
Any Nikon 35mm SLR: Nikon F4,
Nikon F5
for auto focus bodies, FE, FE 2,
FM 2
, FM3A and all from that line up for even cheaper manual focus cameras. They work with your modern lenses, and they do great.
Any DSLR if the shutter count is not too high. A camera is usually recommended for a given number of shots. For example, my old D80 was covered by warrantee up to 80 000 shots. More premium camera can go up to 200 000 or 400 000 shots without a problem. Most cameras have a counter built in, check it out ! It in good condition from a certified seller, a camera with less than 40 000 shots is a great deal.
If you want a very low light camera for wildlife or sport, even now you can get some used product that perform brilliantly. A
Nikon D700
is fundamentally the same as a D3S. It's a non video version of a D4. Many are dying from intensive professional use, but find an rich amateur who can't live without the latest gear, and get one for half price used ! I guarantee that with moderate use, unless you decide to make video, you'll be able to keep it for a decade with seeing any desirable improvement coming from new products.
Finally, medium format gear. It cost half a car new, and the price of a compact used. It's like a guy selling a Ferrari half price after driving it 2000 miles.
My D80 in India in February. I dare you to tell me you can see a difference between this an any more recent DSLR.
Where to buy used ?
- Ebay: if you pick the right seller (99.9 or 100% happy buyers)
- Adorama: take only item in excellent -, excellent or demo condition. They do deliver quick, but they also do try to rip you off sometime. They once sent me a camera that was obviously broken before packing (they paid back). They also tried, in store, to convince me that an obviously damaged viewfinder was perfectly fine. They overal cover for their crap, but it's a bit annoying.
- B&H: so far superbly happy with them, but they have less choice than Adorama for used gear.
- Amazon: sometimes great used stuff but less choice
- Keh: avoid. Very very dodgy customer service, sometimes months to get delivers a bad product, more to get it exchanged.
for the flower and Nikon 35mm f/2
for the rest. Both lenses I can only recommend.
, and I have to admit, the Canon 5D MKII 
. At this price tag, the Canon 5D MKII 
as the compact camera of my choice. I've also been following closely the new Fuji X line, and now that the X10
has been out for a little while, time for a comparison.
, X Pro1). Those products, even if far from perfect (slow AF, poor ergonomics) are indeed something to the landscape: some of do us want premium compact with terrific built quality. 
are the same. It's like getting the 2012 car instead of the 2011. It's just a marketing thing. So go find a