Leopard geckos are great, they're really easy to care for. Though if you have a ball python and a boa, you'll probably want something a little more challenging. Cornsnakes are okay, and if you don't want "just a plain one" there are tons of amazing colour morphs and a lot of them are nice price-wise (well, depending how much you think is insanely expensive. By nice, I'm saying under 300 dollars) There are also kingsnakes, which unless I'm mistaken, can be properly kept with the right amount of homework beforehand. The people I know who have bearded dragons don't seem to get too many problems, although a lot of people are shocked at the adult size. They go into petstores and see adorable three inch long baby dragons, and buy them. Two years later, they're shocked to have a big old 18-24 inch reptile prowling about.
Of course, I'm NOT in any way an expert, I'm actually very novice. So don't take anything I say for perfectly pure truth. My experience in herps, is only a couple frogs (which died, and that's no boaster for me) currently two geckos, and in a few days, one ball python. I do read a lot, but for actual hands-on experience, I'm relatively lost with anything other than leopard geckos and ball pythons (I always research the breeds I get)
My main advice to you: Go to your local library and empty the reptile section of at least 5 moderate sized books! And then go to a search engine online, and search any of the breeds you're even vaguely interested in- and read through at least 10 websites per species before making a decision.