I bought a cheapo OLP 4-string off the 'bay, it sounded fine but I didn't get on at all with the clubby neck... subsequently bought a gorgeous fretless Jaydee neck from Greenolive of this parish, and now it's fabulous.
I'd imagine a used Ray35 may be the answer. Thought I'd get hands on with one in Guitarguitar in Glasgow on Sunday, but nobody seemed interested in helping out a poor bass player - too many guitards to be helped instead...