Wonderful! Thanks, everyone! I'm having one issue though. It seems to be simple enough, but I can't figure it.
As the characters' levels increase, the next_exp determined by this script doesn't update; the value stays at that amount required for level 2. In case I'm not explaining clearly, I'll give to you my specific example. As stock actors, actor 001 needs 30 EXP to level up to level 2. I increase the character's level to 4 through events, but, when I set a game variable equal to the next_exp determined by this script and then display that variable, the variable is still 30.
Did I do something wrong?
EDIT: Ah, nevermind. If I'd just waited a few minutes before posting, I would've figured it out without having to ask! Thanks, everyone :D!