Check around your local Wal-Mart. I found a temp/hygrometer combo for less then $3.00 while on one of my late night Wal-Mart trips last week. I bought the last 2 at my local store.

It's made by a company called Springfield and I found it close to the hardware section with the other temprature/humidity guages. Its +/- 5% on the humidity (which seems kind of high) but for $3.00 you can't really go wrong.