Small video camcorders have miniature mics that do not perform well. However, an accessory mic could run from $5,00 to $500.00, so there is a big spread to content with. There are a few reasonable hand held mics in the $10.00 category, but they are fairly large. The Samson "Go Mic" ($40-$60) may be able to clip onto the flip camera and provide better sound quality.
I have not tested this unit, but Samson is a reliable Audio company.
There are a few really cheap plug-in mini-mics on the market, I have not tested them either.