What will be in the music that necessitates the subwoofer? Backing tracks / drum machine / set break music? I'm not trying to talk you out of it, just simplify the search.
I've found the Yamaha DXS12 is a good in-between sub for bar & restaurant gigs. People will knock it for having a relatively narrow bandwidth and a somewhat high F3 point, but if you need to drive some kick drum and some bass into 100 people or so, it does a great job without taking up too much room in the car and without taking too much out of the bank.