As Ronnie mentions, it can be done.
I also own a 2005 Ford F150. It's the STX model; not much in the way of creature comfort options. It had cloth seats (yuuk), and I wanted either vinyl or leather. I found a set on Ebay (a salvage yard; many post items for sale on Ebay), shipped to a businees with a shipping bay nearest you for 300 bucks. This was 2 years ago. The market for 2004 to 2009 F150's is now flooded with great used parts; soon our 2010 to 2014 Mustangs will be this way. Bargains can be had now though.
Just be sure your current Mustang has the correct wiring to support the power seat(s) and other options you are looking for. So far, no one else has chimed in to this post that has done what you want to do, so you will most likely want to remove the seat(s) to check for the harnesses you will need. Easily done to remove a seat; 4 bolts. Remove the rear bolts first by sliding the seat all the way forward, then slide it back to remove the front bolts.
So far, I have replaced my front bumper cover with a GT one, the rear lower valance from a GT500, the front upper grill from a GT, the lower front valance from a Boss, and all these parts are used. Compared to the cost of new, even with shipping charges, I've saved at least a couple grand compared to new price cost. It's also a good thing when you have a son who works at an auto collision repair shop, and is a painter