Just for fun lets use some known values and ballpark this:
(Mustang prices based on KBB 5/2008)
Mustang Deluxe Coupe: MSRP $20,445
Mustang Premium Coupe: MSRP $21,675
Mustang GT Deluxe Coupe: MSRP $27,035
Mustang GT Premium: MSRP $28,215
Approx. LPV (Lutz Premium Value): $1,500
Camaro V6: Mustang Deluxe + LPV = $21,945
Camaro V6 Nicely Equipped: Mustang Premium + LPV = $23,175
Camaro V8 Base: Mustang GT Deluxe + LPV = $28,535
Camaro V8 Nicely Equipped: Mustang GT Premium + LPV = $29,715
(
http://www.crateenginedepot.com)
LS3RP (LS3 Retail Price): $6,195
LS7RP (LS7 Retail Price): $12,999
Camaro FI V8: (Camaro V8 Nicely Equipped - LS3RP) + LS7RP = $36519
Yes I know GM doesn't pay retail for their engines, and no they're not using the LS7 as far as we know. The current LS7 crate motor makes a nice price benchmark for a 500+ hp LS series engine.