I'm also looking for a solution that will connect the Raspberry Pi to a coin acceptor, but for a different purpose of controlling usage of a internet-connected public computer.
The closest proof of concept i've come across is Nick's Advice Machine http://blog.notdot.net/2012/09/Penny-for-your-thoughts
Unfortunately, although Nick answers questions from his blog visitors, he hasnt yet provided a step by step tutorial on how its built. A plus if he does it on Instructables.
Can anyone provide a better tip on how to link-up a Raspberry Pi to a coin acceptor via its GPIO using Python?