I've bought mine from Monster Guts for years and always been pleased with them. Pick up the quick connector as well as it's money well spent for the convenience.
Likewise with Frightprops and Monster Guts. For a dollar more I would suggest getting a wiper motor with a parking brake. You would never know when your going to need it for a particular prop. I don't buy any of the fancy brackets out there, though it has it's purpose. I either use a Simpson Strong Tie pipe grip tie or make my own bracket.