It was during a promotion, which i've seen come up again since I had mine done. $49.99 ea for E2 and SRT mods.
There is an SRT kid on gunbroker now with a starting bid of $80 - I have not yet seen the E2 parts available for separate purchase.
Glock 19 G4 BFG | Glock 17 G4 FDE | S&W M&P 22 | S&W M&P 45 | S&W M&P Shield 9 | Ruger GP100 4" | Sig P226 MK25 | Sig P229 Extreme | Sig P320F | Sig P320C | HK USP 9 | HK USP 45 (Tan) | Walther PPQ 9
Daniel Defense DDM4 V4 | Arsenal SGL 21 | ASA SBR | Savage Mark II FV-SR
Mossberg 590A1 20" SP | Mossberg 500 Cruiser