Just fight the fish monsters at the beach by Balamb to get the AP. If you get card mod, you can use that to keep your XP down as well as using the summons to kill them.

It is a grind, but beating the spider bot is an extra challenge anyway.

Btw, make sure you attempt killing it when you reach the end of the town sequence. Beating it has random encounters start up again and those will affect your score as well. You'll also want to be there to maximize your timer. Likewise, ''beating'' the spider bot and running away still gives you 50 AP so you can technically farm AP with it as long as you're powerful enough to shave off 25% of it's health quickly so you don't run out of time.