Hello.
I can make that project for you.
For this project the most effective way is using of Arduino (5$) and SIM800 GSM module (approx. 5$) and some software at .
If you are not good in electronics, I can propose a version of the same hardware, but much simpler in connection.
In that case SIM800 module will cost about 8..10$
I can write a software for PC for the convenient sending USSD commands and automated receiving of the answers.
If you want to add some simple database for this (phones/credits transferred/communication log) - that's also discussable