Help with choosing components to RFID project

Hello everyone!

I'm a .NET programmer who has never done any electronics. Arduino looks cool and well documented, thus i'll give it a shot for a project I have got myself into :)

My task is to build a solution that counts lunch coupon's in a sort of a dining place or a soup kitchen.

On the counter there is a "plate" on the table (the antenna) where people place the cards or coupons (reusable) Around 30 cards need to be read in anti-collision logic when they are placed to the plate on top of each other one by one. Then the pile is removed and the count starts all over. Pile of cards is max 4-5 CM high, this is the needed read distance.

Which reader, which antenna and which tags would you use for such application? The budget to hardware and ~500 tagged coupons (can be stickers for self made coupons) is roughly $120-150. If you see it should be done with more expensive equipment, please point me to understanding the logic behind this too.

Thank you very much in advance.