Using the existing system for currency, We are looking to have a system where you can purchase a plot of land, home or more.
The current system requires that you trade a item or such. With such we would need a trade block that is capable of just setting a purchase price and they can pay it.

Basic functionality:
we would need a trade block that is capable of just setting a purchase price and they can pay it. Once paid it could do nothing, output a redstone signal or keep a log of date/time.

Advanced Functionality
The system could be based on a set timer so that x days/hours/seconds and the block would reset so they would have to pay again.
It could allow OPS to output a command on reset as well.

If you just need something that outputs a redstone signal, why not use the Paygate? It lets players "buy" a redstone output (for a defined duration up to 1 minute) from said paygate.

And if you need a time so that they can only pay every X time units, just add the Player Trade Limit rule to the Paygate, as it allows you to limit them to X trades for every X period of time.