If all you need is a card to tide you over then there's no point in paying much for one.
Your first bet is to just ask around, friends and neighbors may have your replacement part sitting in a parts box and you'll never know till you ask.
Failing that both Amazon and Newegg still carry AGP cards, don't look at anything over $50.
You need something like this : http://www.amazon.com/EVGA-256-A8-N3...8205270&sr=1-7
or maybe this list from Newegg : http://www.newegg.com/Product/Produc...25%20-%20%2450