Amplifier w/swappable OP AMP (speakers)?


I am wondering if anybody knows of available options for an amplifier to power speakers. I am looking for something in which I can swap op amps (rolling). Price cap is probably around $250. It doesn't have to be a finished product per se. But assembly from scratch is not something I should be doing--my soldering skills are barely existent.

Any suggestions you can provide would be appreciated.