If I wanted to order several stripped lowers from one website, let's say 3, and ship them to an FFL, do I have to pay the transfer fee on each one, so three fees, or is it just one fee for the whole bunch?
How much you pay is entirely up to the receiving FFL. If you go to gunbroker.com, they have a "find a FFL" function on their home page. Plug in yer zip code, pulls up FFLs that have registered as being willing to serve as a transfer FFL. Most list their fees.