Budget Travel - Transportation from Tuscon to Guaymas area

I need to travel to San Carlos, Mexico (near Guaymas) with some personal equipment so I can not take a plane or bus. There’s just too much stuff. I’ll be coming from Oregon probably in a rental car and I assume I’ll need to switch to another vehicle in Tuscon. I need to either rent or arrange for other transportation like a small car or pickup truck, When I rented a car in San Carlos going north to the US, they were going to charge me $500us to get the car back to San Carlos. I found a local to drive the car back for a lot less. I’d like to avoid the “return” expense if possible. Any ideas/contacts for this trip would greatly be appreciated.