Pete,
You will definitely need to follow Jens advice. Pick your beasties first as the enclosures will need to be very different for different species. Try GeckoDans website, it has some great pickies. Make a short list and then check out prices. Also consider where they naturally occur. If you get something local to your area you won't have to spend as much on enclosure costs like heating. When you find something you like and can afford, you can ask the folks here for specific advice on your chosen beasts. I have started with Lesueurs and am glad I did. They use the whole tank, including running along the underside of the lid!!