I oversaw all my parents' medical bills when they were on Medicare and Social Security. They didn't carry gap insurance, but chose to put that money in the bank and pay the deductibles themselves and probably in their case, it was cheaper for them. Whenever they were hospitalized, the hospital would always send a packet of information for applying for extra assistance if they needed it. Medicare repriced all the charges, sometimes significantly, but you probably already know that. Daddy's last hospital bill was over $100,000, but Medicare only allowed $15,000, and they paid most of that.
If I were you, I'd contact the hospital or infusion center's financial office and talk to them about what's available to you in the way of financial assistance to cover costs of the infusions.
56 yr. old--CD over 44 yr. Hemi-colectomy '01; spinal cord injury '01; fistulae since '97; enteropathic arthritis, chronic pain, muscle spasms, scoliosis, rotator cuff injuries