There is a guy selling an v4 SI Mag for $125 on here. Looks like its in excellent condition from the pics. I dont know him, so I cant vouch, but you can search for his thread.
You have a Porsche and wanting to cheap out? Doesnt make much sense since you should be able to afford what fits your application best, not some random WTB for any cheap shallow 10" or 12" subwoofer