timer disconnect monitor

Looking for a device that will disconnect a computer monitor from computer. Idea is put this device inline with monitor cable between monitor and computer. A simple timer that will allow user to pay in order for monitor to be on. I also am looking into having a card reader so can use a credit card to pay to use. I know of a few apps that will put money on a credit card as a person performs certain tasks. Basically it is a work to play idea. Work get paid, use the pay to play on computer. The timer circuit, and cutoff seems simple, just not sure how difficult it would be to add the credit card for payment. Alternatively I could make an app that does not use real money, makes credits for working, then the credits could be used to pay for time to turn on off the monitor. I this case I would need the box to be able to connect to phone and/or computer in order to send the credits to the box to turn on the timer for monitor. I have an idea just not sure how to go about getting it made and costs. If pay is too low let me know. If I am at wrong place let me know if there is another company that can help. Thank you