I can attest to how nice a 10" sub can sound. I had a sealed 3 cubic foot box with two RF Punch 10's being modestly driven at 75 watts each. Plenty of bass, would bottom out nice a low... was a bit overkill for my application (kept mistracking the CD player). A single 10" in a well built box should work well.

As for the price... he never says what brand the 10's are (it does matter). Find out what they are first... you never know, they could be one of those "subwoofers" at the RV shows that sell for $10 new.