Don't buy cheap tires.
What type of driving do you do with it and how long do you want the tires to last?
My best advice is to get good tires, brands don't matter much as long as its a good brand, chances are if you haven't heard of the company that makes it, they aren't that good. Bit in a 20" tire, you don't really have too many crappy tires to choose from.
If it is a daily driver I would go with a good all season or aqua tread. If you like to drive aggressively and don't mind them wearing fast, go with more of a race tire but unless you really push it hard, most any all season tire should be plenty.
Sorry for such vague advice