Our 17 year old wants to buy one for around $3,000. The mechanic says he know the car. pros and cons

Often see these cars go 200k miles or more. Safe cars too. If you are concerned about the lack of air bags sounds like you aren't teaching about seat belts. Teach them now to use them. Have always use mine and require all in my car to use too. My first car was a 62 Chevy PU without seatbelts. Got a Camaro at 17 and have used since. Taught my kids to use also.