OregonMouse....thank you very much for your comprehensive reply.
I checked Rent-A-Wreck and their prices were the same as the first tier rental car companies. However, (and here's a tip) somebody replied to my similar post on a backpack group on Facebook and suggested that I try Turo. Bingo!!! It is an app/website that appears to be the "Uber of rental cars" in that they organize and connect people willing to rent their vehicles to people needing a more economical option rather than going through large companies. The rental cars are even insured by Turo. I found several options including a Ford F150 (not that that's my choice) for $17-$23 per day. It looks like the mileage is limited and set by individual car owners, but I won't be putting a lot of mileage on it anyway (hopefully, I'll put more miles on my boots than the car).
I like your suggestion for your described transportation links to Stehekin and the variety that a ferry ride provides. Of course, if I go there I will check out the bakery.
I haven't decided, exactly, where I plan to go although I know what I am looking for. I am a photographer and I would like to experience the wildflowers, alpine lakes with the good early morning or early evening light, vast vistas of peaks shot almost at their elevation, and the feeling (at least part of the time) that I am waaaay out there. The top of my list includes Sahale Arm, Maple Pass and Lake Ann area, Rainy Pass. I don't have all of the other names memorized but, generally, some the higher areas of the PCT east of Ross Lake, possibly Snoqualmie Pass and Stevens Pass. I still have a lot of research to do before I determine my final itinerary.
I will check out those other local forums that you suggested.
So far, my dates are August 2-23 so I suppose that I won't have much problem with snow on the trails.