The Panther mounts are kind of the industry standard, very good quality and reasonably easy to get your hands on. I've got the "Static Motor Mount Plate Model 405" for both my Vantage and kicker and I've been very happy with them.
If it's an older boat and you don't care about appearance then you may just want to get some metal brackets, screws/bolts, and a chunk of 2x6. It will do the trick but doesn't look as pretty as the manufactured ones.