Air Ambulance Service & Hospital Bill

Date of service was 10/03/03 and state was Arkansas. A fall at home resulted in a facial laceration and trip to the ER. After a CAT scan (that revealed a possible subdural hematoma and was later diagnosed as a benign meningioma) ER doctor recommended air ambulance to a larger hospital in Missouri about 45 miles away. We presented our membership card to Air Evac (that would have provided air ambulance to me free of charge) to ER personnel in Arkansas. My husband signed a consent for transfer with Air Evac. Later, ER personnel came back to tell us Air Evac could not be dispatched due to fog and Hammonds Lifeline at St. John's in MO (the hospital I was transferring to) was coming after us. They did not mention cost and we assumed they had a reciprocating agreement for these circumstances. ER crossed out Air Evac on the consent and entered Hammonds Lifeline without obtaining my husband's signature or initial for the change. St. John's Hospital submitted a bill to us for $6,500. After a year of negotiating with all parties directly, St. John's agreed to discount 30%, the hospital in Arkansas has agreed to pay $2,200 if we sign a waiver releasing them of any further liability and St. John's has sent us another 10 day collection notice. St. John's has told me they are using the consent from the originating hospital to pursue this debt. Should we make payment arrangements on the remaining 2,300 with St. Johns or perhaps hire a lawyer to pursue further. Either with St. Johns since in my opinion they are using an altered consent form, or with the hospital in Arkansas that has already admitted some liability?
Tried to be brief...but facts are complicated.
Thanks for your help.