well...i wouldnt exactly jump into a moter yet, unless you really want to make your GT into a GTP. I'm just gonna warn you, its not a real easy job
i did it to my SE.
the tranny will work, but w/ your car having 98K on it, i guess it depends on how much you took car of the tranny, will the tranny last you
the GTP comes w/ a 4t65e-hd version, where as your gt has the non hd version. the hd is just a little more built up. My SE still has the original tranny in it...and is still shifting strong, considering the fact that i have a ZZP shift kit, and Desert Fox transmission cooler.
i was lucky, and found a supercharged 3800 motor w/ 60K on it in the junkyard that my dad deals with for $1000.00 shipped, but he also owns an automotive business and deals w/ them regularly.
shop around and see what you can find, but you should expect to pay anywhere from $2500-$3500 for a decent motor.