I've got a client with several 2450 (2.4 GHz) PMP100 legacy APs & SMs needing replacement

I've got a client with several 2450 (2.4 GHz) PMP100 APs & SMs needing replacement, after having worked reliably for many many years. As the PMP100 is now EOL, what is the best and most economical alternative using a Cambium Networks solution? I realize a drop-in replacement with the PMP450 won't be possible, due to compatibility issues, but I'm trying to find the most palleatable solution for them. Thanks in advance for your input.

You could swap them over to 2.4 450s.  The 450s support a fourth channel in the higher end of the spectrum than the PMP100s do, so you could put up 450 APs alongside the PMP100 ones to allow SM swapover without downtime.

Why do they need replacement?  If the units are failing, I'm sure replacements can be obtained used for peanuts.