I bought over $50 worth of stuff (a nice multimeter, a heat gun, some other things) so it was free.
Here's their shipping rates for the US
up to $14.99........$2.95
* $15.00 to $24.99....$3.95
* $25.00 to $ $39.99..$4.95
* $40.00 to $49.99....$5.95
* $50.00 and over FREE*
I took a look at Greg Covey's article on converting the Harbor Freight 'Lightening'--
It looks to me from the pictures that the motor and related gear are the same, so probably a very similar conversion would work well?