It sounds like you have a type of insurance that is there basically to kick in for catastrophic scenarios. Those types of insurance charge cheaper monthly premiums. So it's a case of pay more in premiums, or pay more for your care.

Is there an option where you could pay a somewhat higher monthly premium that would cover more of the costs of getting treatment?

The costs you are describing would, indeed, make it very hard for most people to afford the care you've been getting.