I roll with a 450 watt E-Zee hub motor w/LIPO4 10AH batteries. I paid <1600 complete from a reputable (highly recommended) online vendor (with a brick and mortar shop in North Carolina). It is installed on a Kona Fire Mountain Xtracycle ~ $500 for the bike + ~400 for the Free Radical attachment.
I have been very happy with their service. I would highly recommend them. I didn't mention the shop by name cause I am not sure if that is allowed. I am not affiliated with them in any way, other than as a satisfied customer. I ride it every night.