What is the voltage limit on SKY130? I want to try and build an integrated motor controller/gate driver that can do up to 80-100V

You should take a look at :https://skywater-pdk.readthedocs.io/en/main/rules/hv.html#failure-mechanisms-in-vhv-devices

@User: I cannot find any P-N junction breakdown voltage values in the SPICE models for parasitic diodes in the process, but generally that breakdown voltages is going to be between 20 to 30V. Typically, to get anything above that requires a special process, namely SOI, so that all diffusion areas are isolated by insulating material with a high breakdown voltage, not a P-N junction.

I suspect skywater can do SOI but it has probably not been released to the open pdk