I like colubrids like Corn and King Snakes, I just got mine and she is easy to care for and has been cheap to care for beyond the initial expense($75 for the snake, and another $30 for the tank and care package, $20 heat pad and emitter, and some cheap aspen bedding). Things can be cheaper at reptile expos, where I got my King Snake and viv.
Ball pythons are cool and good starter animals too, but are prone to food strikes where they could refuse to eat for months at a time. They also require more strict humidity requirements than king snakes and corn snakes as far as I've seen. But they ARE much easier to hold, an acquaintance has one and he is a joy to hold. My king has acclimated to being held though, she's much better than she was a few months ago.
Some people prefer pythons, some prefer colubrids. It sounds like you're leaning more towards a colubrid there. For what it's worth, I plan on getting a ball python for my next snake
Both are great animals.
$900 is much more than enough for starting a python or colubrid with a tank/tub and supplies, as long as you don't get one of the expensive morphs. Even if you did buy an expensive morph for $100-$300 you'd have more than enough left for feeding and supplies. I'd suggest getting a less expensive morph for your very first snake though.
Remember to give the snake a thermostat and some sort of heat source, like a pad or light! But not heat rocks, those can burn your snake. Put the heat pad/light/emitter on one side of the enclosure, so that the snake can choose between being warm or cool, and also one hide on each side for a total of 2(at least).
EDIT:
There is a reptile Expo in Corpus Christi in August!