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.
NASM is top notch, as is ACSM. I’ve read the NASM book cover to cover and its OPT model of assessment and programming is a thing of beauty. I know ACSM is well respected but I haven’t read their book.
Another PT cert that I think is fantastic is PTA Global. I have attended workshops by several of the people who designed the PTA Global cert and they’re talented practitioners as well as presenters.
I have ACE and have had it since 2009. It’s been a good certification, and my job opportunities have been plentiful. If I had it to do over again, I’d do NASM or stick with ACE. I was 2 weeks from my NASM exam when I got a job that needed my attention. I’m glad I took the job but I regret not sitting for NASM after all the prep time I invested.