There are Ford ESP's (extended service plans) ranging from 3 to 7 years, 36K to 100K miles, 4 different levels of coverage, and 5 different deductible options. This is a huge matrix of possible prices with 500 possible combinations!
That said, a GT500 will have a supercharger surcharge. Waiting to buy until after 12 months or 12K miles will invoke a surcharge. Buying in the first year is the cheapest way to go.
Also, the most common plan (bumper to bumper, 5 years, 60K miles with the standard deductible) is priced around $1,200 to $1,500 on a GT500 at most decent dealers. When you start pushing the years and/or miles up, Ford is banking on more likelihood of needed repairs, so the cost of the plans goes up dramatically - especially on 6 or 7 year plans, and on 75K or 100K mile plans. So, considering that twin turbo is talking about a 7 year plan, then $2,500 starts to sound more reasonable (especially if it is a 75K or 100K mile PremiumCare bumper to bumper plan).
My wife and I both work at a Ford dealership. We bought a Ford ESP for her SUV a few months ago. Essentially a bumper to bumper 7 year plan (60K miles) and our cost (as employees) was $1,500 for such a long, comprehensive plan. Warranties are not cheap, but they can cover so much that we always buy them for our vehicles.