I would be concerned about UIUC PREP after reading this from the director of admissions:
“As much as I hate to write this, if a student admitted to PREP only wants to pursue a degree in Bioengineering, Computer Science, or Mechanical Engineering without considering any of our other highly regarded programs, I would strongly encourage that student to enroll at another university”
Aero is only one tier down from those three in terms of difficulty to transfer in.
Purdue allows you to choose a Major after the first year, and 90+% get one of their first two choices. After that, transferring between engineering majors can be difficult. Especially into MechE or Aero. But you do have a full year to make a decision.
GT is a great school, and might be a better choice without financial considerations. But I’m not sure the money gap makes it a better choice than Purdue.
(Disclaimer: my D is a 2nd year MechE at Purdue)