For 400$ an old K5 is - IMO - a very good purchase - I'd buy it in a heartbeat. The first models had a sandwitch padauk/mahogany/padauk body with wenge/walnut neck. Ignore the K5 inlay (although I think it's cool) and maybe replace the gold hardware with black stock hardware and you'll have a killer bass. In spite of being designed to sound mid scooped (Fieldy's sig tone), the bass is still pretty versatile and you can get a lot of tones out of it.
As for non sig Ibby basses, a SR500/505 would be a great deal too, if you can find one cheaper than the store price. In general any bass higher than that in the SR/SRX/SRA/SRT/EDB line would be a good purchase.