need wireless for 8 buttons

I've been playing with arduinos for a while but have never done anything wireless. Now I want to send the status of 8 buttons (where multiple buttons could be pressed at once) back an arduino mega. It needs to be wireless and the max distance will be 20 feet. It would be extremely nice if the transmitter with it's 8 buttons would be battery powered. The buttons will be mounted on a stand where there is room for a largish battery. What are my (cheapest) options? FWIW this is a hobby project.

What are my (cheapest) options?

Price vs. ease of use appears to be fairly linear. Where on that line would you like to be?

I'd spend $50us and be ok with it.

This would be pretty cheap:
Promini, scans all 8 button, sends message via 434 MHz Tx module back to the Mega.

Have it go into power down sleep mode to save battery life. A diode from each button ganged together to the interrupt pin to wake it up & send the button press results. (cathode to button, anodes to the interrupt pin). Button pins use internal pullup resistor, button press connects pin to Gnd.
Send results via VirtualWire.