You can go to a Staples or Office Depot, they have more info on their websites. Vistaprint is good because they're cheap but they can be crooked/flimsy, GotPrint.com I've found is the best quality and still very reasonably priced.
Also check for discount codes at Retailmenot.com if you purchase online.
(If you want to get real crazy you can sign up for Ebates, then order your cards, enter a promo code and get an even better discount!)
Good luck at your show!