Linux Kiosk with timer driven by coin collector

We have the need for some Kiosks that run with serial/usb coin collectors to give users time online and a countdown timer. The systems will need to allow for free access to a walled-garden list, then be told they need to deposit coins into the system to access anything else. I would like this to run on Centos/RedHat/Fedora as that is what I am familiar with. I would also like to have the system itself be able to be set up as a read-only filesystem. internet will be supplied via router with DHCP, so nothing special will need to be done there. The machines will have standard keyboards/mice as user input only and will NOT be connected to printers or the like.