20W should be enough for most applications in a smaller room, if your speakers are reasonably sensitive.
Here is a calculator to give you a rough idea: http://www.hometheatrebasics.com/home-theatre-tools/spl-calculator/
There are a whole bunch of cheap Class-D amps on Ebay and Amazon which should be more than adequate. There are also some that would put out more power, but without knowing your environment and speakers, there is no way to tell if you need it.
As far as reliability..., for $50-$100 you should be able to get something that lasts for a while.
I still have a 100WPC Tripath Italian-made amp, which has lasted for about 3-4 years now (although it cost something like 400 Euros back then). And that's an Italian-made electronic device....