well hotswap + iso i have not found
and < 100 i have not found either
(at least nothing good, a DK87 + gateron swithes + cheap caps might be under but you will not have that great of a keyboard and not that much under)
iso is really unpopular here (for some reasons), some peoples do seem offended to even the mention of a keyboard not being ansi, personally i made the compromise of using soldered switches and still i reach much higher than 100.
if you do not mind it not being custom you could get a gmmk, they exist in ISO are hot swap-able but come pre-built.
you could also build it from scratch, there you will be able to have all the features you may dream of, but it will be much harder, but can also be much cheaper (if you have the tools and know-how and a spare piece of wood)
and all of that also heavily depend on the size of board you want, 100% is unpopular so you will have very little options, TKL slightly more popular, 60% is the most popular so it is where you may find what you want, and is also the cheapest (because there are less switches, less caps and a smaller pcb and case)
hope this can be of use to you
