How hard is it to achieve great photographs? Not very. There is a little bit of work involved, but as you're spending the time to build your models in the first place, a little effort for photography isn't much to ask for. How expensive is it? You probably have all you need already.
In order to provide in-depth tips, I am doing this as a series and each week (hopefully) I'll post an article relating to only one part of the process. There are many guides available at most forums that are all-in-one stop shops, so if you're completely lost on LEGO photography you may want to use one of those as your main education and treat this as additional help.
Week 1 : Is my camera good enough?
With the digital revolution well established, the choice of camera has become an even more complicated process than before. Back in the glory days of film, a camera was only as good as the film put in it. This is probably why film cameras have a longer life span than digital, there was just much less to them. This also presented you with a very large selection of results depending on the type of film you may have used. With digital many users are prone to taking the pictures straight from the camera and doing nothing to them. While they may view this along the same lines as not editing prints they got from film, one must consider that your digital camera only has one sensor and the number of ways that sensor can capture colours differently is severely limited. I can't imagine using the same film all the time, therefore I can't imagine not doing some sort of processing to my digital images!
Anyways, getting back on topic, with the limitation the above mentioned one must be careful when purchasing a digital camera. Your first big decision will be between a Point & Shoot or a DSLR. You're not training to become professionals, so a Point & Shoot will do the average LEGO builder fine, therefore, I'm going to focus first on the Point & Shoots and then touch base a little with DSLRs later on.
With a point and shoot you have one lens, so you better make sure you've got good quality optics! It all really depends on what else you may be using the camera for but consider the following: large zooms will not give you as sharp photos as smaller zooms, there will just be more glass in there; watch for "optical zoom" and "digital zoom", the former means that the lens is actually moving to zoom in and the latter means that the camera is just cropping the image - the former is thus much preferable, digital zoom is a cheap gimmick best avoided.
For photographing LEGO there are some key features you want: Exposure Compensation and White Balance. Aside from those, you won't NEED any other controls. Many Point & Shoots might not have specific White Balance Control, but will have different shooting modes (indoors, outdoors, night, snow, etc.) that are set with different white balances - if your camera has these, experiment and see which one gives you the most neutral whites when photographing your LEGO models. Don't get carried away with Megapixels, and don't choose one camera over another because it has more. The actual image sensor on a Point & Shoot is much smaller than 35mm film and it is the size of the sensor that matter more than how many Megapixels you have. 6 will do fine. Anything more, and your just trying to see how many people you can cram into a phonebooth. Bad idea. You're just going to end up with more noise/grain.
Marco is an excellent feature present on many Point & Shoots and will allow you to get very close to your Model when the feature is activated. KNOW how close your camera can get to its subject while remaining in-focus, and don't exceed those limitations.
With all that said, most Point & Shoots will work fine as long as you know how to use them and are doing so properly. Always read your manual! It will provide good camera specific information that you need to understand.
Now I'll touch a little on DSLRs. If you're interested in photography aside from snapshots of your LEGO models, you may want to look into one. However, if you are unfamiliar with how to take a photograph manually then I would recommend you purchase a used 35mm film SLR and learn the basics from there. 35mm film and equipment can be had very cheap, and older equipment is very reliable! The less electronics, the longer it will probably last - I have cameras from the 1920s in perfect working order. Some people like to think film is more expensive than digital but they ignore the low cost of older and used SLR bodies and the high cost of DSLRs that will probably be in need of replacement much quicker.
Regardless, if you know about exposure and manual controls, and have access to a DSLR you can take very good photos of your LEGO models! More control over image taking will result in you being able to respond to different situations much easier. You will have access to Exposure Compensation as well as Manual Exposure and proper White Balance controls. If you are shooting your models on Manual, make sure your aperture is set to a relatively high f/stop to make sure all of your model is in-focus. It depends on the model's size, your focal length, and how close you are, but you don't want to be shooting any more open then f/5.6.
Many of the things I said about Point & Shoots applies here too. Sensor size is much more important than Megapixels. DSLRs are slowly becoming fitted with Full-Frame sensors, which is fancy terminology for saying they're finally the same size as 35mm film. Most DSLRs still have APS sized sensors, so again 6mp will do just fine. Don't overspend for features you may never need or use.
When choosing a brand, know that they will all perform splendidly. Don't listen to anybody saying one is better than another, they're speaking out of their rectum. Consider if you have any old lenses, if/how they can work with a modern DSLR, the selection of lenses the company offers (will they suit your needs?), compatible flashes, what type of memory card (all mostly CF), but MOST importantly - how does it feel in your hand? Go to the store or find a buddy with one and feel them out.
That ends Week 1 of LEGO Photography 101. With all luck I'll move on to our next topic next week which will be the shooting environment!