It's not that expensive here. You can get 3,5,10M baht comprehensive coverage here. With no claims in 4 years my 5M baht coverage is 2,000USD per year (mid-60's).
I agree on finding a local insurance broker, they will give you options (if any) for your mother and costs. Self-pay, at either a Government hospital (much less expensive) or an international hospital is the other primary option. Or, if she can travel, even returning home for a procedure could be an option.
The 5-year ban likely overrides the court 2-year ban and aligns with immigration law. Only an immigration lawyer will be able to tell you if there is any chance of returning sooner. If you can't get entry, someone suggested maybe living in a neighboring country (Vietnam/Cambodia) if that is an option for you for 3 years or occasional visits with your gf/baby. Good luck!