In the PC version of Spelunky, I don't know what buttons to press to pay the Tunnel Man. How can I pay him?
Press up and down to change the amount of money you're offering him, then press your default 'use' key to pay him. The tunnel to Area 2 costs $100,000, the tunnel to Area 3 costs $200,000, and the tunnel to Area 4 costs $300,000
From the PC wiki.