I wonder if there are fast ways to get there from Sofia without having to fly or rent a car?
Maybe rent a driver? Are there coach companies that serve Sofia - Tirana and Sofia - Podgorica routes at all?
FlixBus does those routes. Sofia to Tirana in 11 hours; Tirana to Podgorica in 3 hours.
I've been to all 3. I wouldn't look forward to long bus rides in any of them. I know some good guides in Bulgaria, Albania, and Montenegro. I suspect one or more of them would have some experience with one leg or another. PM if you are interested, and I'll send you their contact info.