Screw that price, for 18k get Mach 1. Around here 04 GTs are in the 14k range. Mach 1s in the 17.5-18.5k range, 99-01 cobras in the middle.
As for conversion prices for body parts.
550ish for 03/04 front bumper, lights, brackets etc. then add $ for painting - discontinued like the 99/01 so they are getting sparse.
285 for the 03/04 rear bumper cover then add $ for painting
Skirts mine were 300 painted and shipped to the house, $ varies a bit by color.
300 for the hood then add $ for paint
Badges - dont, either shave them, get something like a 4.6 or 281, or leave them alone.
Those estimates are on the low end, expect to pay even more than that. Also, add the parts listed below
$400 front brake kit w/ calipers
$200 rear cobra calipers
$180 rear brake conversion kit w/ brackets
$1,000 front and rear seats
$200 cobra steering wheels
$300 rear view mirrors
$300 rear spoiler plus cost of paint
$100 grill delete with cobra emblem
$40 pair cobra windshield wipers (yeah, they're totally different from the GT)
$30 pair of cobra gills for the side scoops (also different from GT)
and after all that money spent, you still have a GT. in order to justify all those 03/04 Cobra visual mods, you must then upgrade your engine to match the performance of the 03/04 Cobra.
$3500 forged short block
$5500 Kenne Bell competition
$2500 T-56 to handle the power
$1000 built rear end to handle power
$800 03/04 cobra gas tank and pumps
plus various other things as well as installation cost. so that comes out roughly around $18,000 in order to PROPERLY clone a GT into a 03/04 Cobra.