What you're asking is sort of like "what's the best car I can get for $500?" Much like the car, your options are gonna be quite slim. Using plain old copy paper leaves you with a bevy of brand choices, and that's about it. I'd recommend saving up for something that a) is the right size and b) is better quality.
Otherwise just close your eyes and grab a pack of copy paper. It really does't latter which you grab.