You can't buy the stripped bushy lower direct from bushy - they sell only to FFL dealers. Gunsmoke will sell you one for a reasonable price, but you'll have to get it transferred to a local FFL who will probably also charge you a transfer fee.
The complete kit can come directly to you.
You basically save on the FET, which is only assessed on complete firearms, and not on stripped lower receivers, and would comprise 11% of the wholesale price to your local dealer.
As to whether this will result in you saving any money over an assembled rifle, that depends on what your local dealer sells complete rifles for... Plus, with a complete factory rifle, you get a warranty, which is something you don't get by assembling a kit and stripped receiver yourself.