Hardly. Average price for a loaded GT(which most SGT's are) is around $30,000. Adding $10,000 puts you at $40,000. Most SGT's sticker for around $37.
Add up all the parts AND labor costs and you'd be right around $37K.
I have a fully loaded 2006 Mustang GT with mods.
Here's what I paid...
FRPP Stingers = $400 to $500? Easy, free install you can do youself.
CAI and Tune = $600. Installation is zero. Very easy.
Gears, Parts and Install = $800. My local Ford dealer did this one.
That's $1,400. I was also able to get 3.73 gears for my auto instead of the 3.55 gears in the Shelby GT. I received a tune from Bamachips, much more aggressive than a factory tune, plus I now have an SCT tuner, instead of no tuner at all. (Very useful tune!) The Stingers have a more aggressive exhaust note than the GTA on the Shelby GT...not necessary for performance, though.
The FRPP X-pipe is $100, I think? There isn't much performance gain (some report losing low end torque), so I haven't looked into doing that. An exhaust shop should be able to weld it in expensively.
I was able to find the FRPP suspension kit (springs, shocks, sway bars) for $1,200 online plus shipping. That's $3,100 in parts so far plus the cost of the FRPP installation.
Let's say it costs $1000 to install the FRPP suspension. I think that's a fair overestimate. That's only around $4k.
You're still $3k cheaper than a Shelby GT. You can use the remainder of the money for 255 series summer tires, new lower control arms and the FRPP brake bads if you like.
I can understand why someone would get the Shelby GT. If you're worried about warranty and don't want to mess with installation, then that's the way to go.
My 3 year warranty expired with about 12,000 miles on the car. I didn't really consider warranty when modding the car, since it's only for the weekends.
Anyway, I think both approaches have merit.