I am about 50 miles south of Columbus along I-71.
Lets see about price.
Receiver maybe $200.
Kit $ 100 up.
HTS $ 50.
Piston $30.
Charge handle $50.
Pistol Grip $ 10.
Mags $ 4.50 (used), $10 new, recently.
Assemby and park, ~ $150.
Excise tax @ 11.5%
Sales tax @ 6% in my county.
These are all cost estimates. There is some variations from source, quality etc. If the guy is a business, some profit should be expected, maybe 10 to 30%, give or take..