i say go for some geckos. probably because i enjoy keeping them the most, lol. but regardless, they are relatively cheap to look after. a basic set-up will cost you next to nothing. (large plastic tub $10-15, a couple of pot saucers $5, a large bag of sand $5-10, a heat cord $20 and your good to go)
a pair of thick tails( u.milli) or knob tails( n.levis levis) will cost less than $10 a week for food as well.
obviously these prices will vary depending on where you get your products, food, etc but it is still not a bad price.
once you get a python or 2 well established they are also very cheap and relatively low maintenance as well. just personal preference i rekon.
goodluck, ian