I have updated this post. I made a few mistakes in the circuit that I designed, and it didn’t work as it should. Make magazine has a great LM386 circuit that is used as a guitar amp. The $5 Crackerbox Amp.
If you want to use this as a simple amplifier for something that is quiet, but doesn’t need distortion, you can remove the 5k pot from pins 1 and 8. Or you can use trim pot and set the gain for at the perfect setting.
Make lists the parts list on their site. I also have a parts list on the Instructable that I wrote. http://www.instructables.com/id/The-Process-of-Building-a-Cigar-Box-Guitar-Amp-L/ It will probably cost more than 5 dollars to make, but it is worth it. It shouldn’t take more than 2 to 3 hours to have a great amp.