It's going to be really hard to find a bass for under $5,000 minimum, like definition said. You might find an older Buescher True Tone or an early Conn for under $6,000 that needs a little work; ie. pads, corks, etc. As for a payment plan, one option might be to look into the LA Sax bass. At least, I THINK they have a bass that sells for around $7000 unless it has been discontinued. You may be able to get your payments down to where it might be affordable, I don't know.