For a garage system that may be in the hot and cold I'd just pick up something off of craigslist. I've had the opposite luck of the poster above and have had very few problems. I got a whole Pioneer silver face system (Amp, tuner and casette player) along with some 12" speakers for $25.the only thing that didn't work was the drive on the tape machine (broken drive belt - they rot after a while). I also got some 12" Cerwin Vega Re30 speakers for $25 and they work and sound great on a Sony AMP the seller left with my house when I moved in.

You can also get a Bluetooth input you can put in your L and R inputs to allow you to use your phone for Pandora, stored songs or whatever on your phone.. Many amp/tuner combos can be had for under $50 and you could probably go though 4 or 5 before you are at the cost of a new amp. Make sure to test it through the volume range before you buy and listen closely for static or dead spots in the controls for both channels.