I'd suggest Craig's List or haunting the used market for a loud-but-ghetto uglier than sin bass rig for cheap $$$, and then flip it when your bassist gets his rig back. IMHO if you don't spend the coin on proper FR gear for bass with PLENTY of headroom, you'll be disappointed, especially if you are looking for a lot of low end THUMP. The caveat here is that you can get away with nothing fancy FR PA cabinets for bass if you're playing small rooms that don't like it too loud to begin with.
I've kicked this can around for years, and most of the time now I use a pair of passive Atomic CLRs and a power amp. In small rooms, this is enough to cover the low end. In rooms with a full PA system that includes instrument reinforcement, then the bass amp on stage only needs to be so loud, and the more low end "thump/boom" coming off my rig, the more my bandmates turn up and/or give me the stink-eye. So I don't really even tempt it anymore and I'm happy with cabinets that bottom out around 80hz, powered by an amp with plenty of clean headroom designed to handle bass.
JMHO