I recently purchased a set up and new baby veiled chameleon in the last couple months. When deciding to build your own cage or purchasing one, it really depends on your tools and time available to spend building the enclosure. If someone has no tools, then it can get pricey to build one. It also depends on Craigslist in your area, which often has great deals on cages. I purchased a baby enclosure for only $20.
I personally used that small enclosure for the first month I had the cham, and then moved him into a large Zilla cage
http://www.amazon.com/gp/product/B000OQSJX0/ref=oh_details_o02_s00_i00 which was less than $100.
I will end up building a custom wooden enclosure for my cham within the next year. Luckily for me, my father and brother are experienced carpenters with all the tools and free wood I would need, so all I would have to buy is screen and stains for the wood.
It's important to make sure the cage is not too big for your baby. When I first put mine in the Zilla cage, I was not confident with him finding enough food and he was not willing to cup feed. That's when I found a deal on Craigslist and saw him eat immediately after I put him in.
Good luck with your set up! I have up loaded some pics of my set up in other posts. You will get some great advice here and feel free to view my previous posts to see those pics.