Well I don't know what to say to that. A ballpark estimate (bankrate.com) tells me that you'll ultimately pay $27,000 less over 20 years even though you'll have $25k more in principle.
By some twisted logic you could say that Gulfstream is supplementing your initial training (someone certainly is, PNC isn't doing this out of the kindness of their heart). That's really tough. Assuming you have your heart set on ATP (for whatever reasons you have), and assuming you can't get a better loan elsewhere or wait for a better rate...you'll be throwing away $27,000 if you don't do the gulfstream program.
I can't fault you no matter which way you go with this. $27,000 is real money, whether it's money right now or money saved over the course of your career. It's also $5,000 more than expressjet paid me for my first year. I mean, is it even PFJ any more? I'm typing this live as I think, so I'm all over the place in my head. We can debate on whether or not someone with 250 hours should be in the cockpit at an airline...but that's a long discussed topic with many threads already on the forums, and not directly tied to this topic (people with 250 hours flew at TSA, and some other airlines).
That raises the question again...who is eating that cost? Gulfstream? ATP? Someone is...