I’m a strong advocate for having a second/backup car. I have one and recently had to rely on it for 5 weeks while my daily driver was in the shop. Of course, I have a ~35 mile commute and no option for Uber or similar alternatives and I know that a lot other people are not as car-dependent as I am.
If you haven’t already, I would have them do a bumper-bumper inspection and look for any and all problems before you make the final decision to sell. A Toyota with 134k miles on it is basically middle-aged; most Toyotas built since the early 80’s or so can happily go 250k miles without needing major engine, transmission, or electrical repairs. You aren’t dealing with a Vega so unless something very expensive like the transmission is actively failing (you indicated this isn’t the case), I would keep the car and repair it.
Further, you note that replacing the car would cost much more than the repair would cost so it’s basically down to a question of convenience: is it worth $1800 to have two reliable vehicles? For me, the answer is unequivocally Yes.
Your mechanic sounds very honest. I would trust them to tell you what is wrong with it, what is good, and what will likely fail in the next ~50k miles. That may help influence your decision. Asking what may fail tomorrow is often more valuable than asking what is failing today.