I didn't see anything in the original post that suggested she was only looking for ball pythons. Just "snakes" in general. For photography's sake, I imagine the larger snakes make a much bigger impact in a picture...but not necessarily the giants. Boas come to mind as an ideal size. Womas or black heads would make for some very dramatic pictures...you don't see those snakes in posters at all!

The problem with such a general question is that there is no real way to pin down how much you could expect to spend. You can buy corn snakes for $10-$20...or spend a few hundred on a nice woma. A lot of snakes can be had for a nominal fee from a rescue. And if you want to get into all the different ball python morphs...well, there's a huge range of prices there, too.

Cost of upkeep would depend entirely on how many and what kind. A single corn snake doesn't cost much to house and feed at all....but a single burmese python requires a very large, secure enclosure with specific heat and thermostats...and their meals can get a bit pricey as they get big. Multiply feeding costs times the number of snakes you intend to keep, and it can add up to a hefty chunk of your monthly budget.

Lastly...if you truly intend to keep snakes for modeling purposes, then all of them need to be carefully selected for temperament and handled on a fairly regular basis to keep them used to and comfortable with human contact. Ball pythons are naturally docile as a general rule...however, they are also very shy and may stress out with such handling. Some of the larger snakes like boas and burms can also be very docile, but you have to work with them to be sure...as well as to get to know them and learn to read their body language...a surprise bite from one of the big ones is NOT fun.