Thats how the air works.
I'll grab my list in a sec.
MR1 - $75
J&J Ceramic 14" barrel - $10
MR3 Rail - $15
RAP4 Airthrough Stock - $30
ACP Bolt $10
Hobby Horse Black Fittings - $16
Single trigger frame from a Spyder Classic - Free
Q-loader system with a couple pods - Free (thanks again PBGrandpa!)
M4 Barrel Shroud and Front sight - $15
Red/Green Dot Sight - Free/on hand from BB Gun that I've had for a few years
2 Rail's for Sight (mounted to MR3 rail) - $3 from local shop bargin bin ($1.50/peice)
Final price, and cutting it close at that, $174.