I don’t know anything about the IACET standards.
Most CPT study materials plus certification exams will cost between $400 and $800.
Your best best on finding out what the best ROI is would be to take a look at the facilities where you would like to work and ask which certification(s) they prefer. NASM and ACSM are considered to be gold standard. I would argue that PTA Global is equally high-quality. ACE and AFAA are also well accepted.
You also have to consider short versus long term ROI.