This Jackson is the only 5-string with reverse P-configuration that I’ve seen. 5-string, reverse P, specific preamp for under $1000 tall order for a production bass. Honestly I think your best bet is to find a used 5-string, then get the bass routed for reverse P configuration and your preamp of choice installed either by a luthier (or yourself if you have the skills).I have never put together a parts bass or bought a neck and body from Warmouth, but you might find a reverse P-body, a neck and then have the pickup and preamp installed. Let us know what you decide to do this is an interesting challenge!