Yeah, kenyan sand boas are adorable and males can live in a ten gallon tank. Snakes can be sexed the moment they are born, so ask the breeder for a boy. Although they are 'sand' boas, I don't like to use sand with reptiles, so I suggest using aspen as the substrate. They do not like humidity at all in their main enclosure, but giving them a humid hide(hide with wet paper towels etc.) helps them when they need to shed!
Get a heating pad to put on one side of the tank, and maybe a heat lamp. Make sure the heat pad is attached to a dimmer or thermostat to keep the temps stable. Have a GOOD digital thermometer (18 dollars at lowes) and make sure the temps do not get too high! You don't want a cooked snake! 90 on the hot side, 80 on the cool.
They need a water bowl to drink, but put it on the cool side, not the warm side. If water is on the warm side it would evaporate and get them too humid and sick! Cool side wouldn't evaporate as fast. Feed them every 5-7 days an appropriate sized rodent(same width as widest part of snake, or just barely bigger)
Did I mention, they are CUTE?
You can convince parents with calm education and care. For instance a kenyan sand boa will barely reach 2-3 foot, max. That's not that big(certainly not big enough to eat you or a cat!
Usually the set up is the most expensive with reptiles, and after that the care is cheap. We buy our rodents in bulk, so a rat comes out to be 80 cents. That's how much we spend on them on food every week. We use paper towels as substrate and then it's just water and electricity that costs money. :) But boy was getting them set up pricy! But it lasts forever.