Used Car Buying Advice

I am currently trying to buy a used car. I am a classic trope: a broke/struggling college student. I am graduating from uni in December of this year. I need a car badly. I only have between 3k and 3,500 total to spend on a vehicle. I see a lot of cars on the Facebook marketplace. I am terrified of getting scammed. I have a few men in my family who know a lot about cars. They are willing to assist me in looking for a vehicle. I have a dilemma. I have been reaching out to potential sellers, and I've offered to pay for a diagnostic test before I buy the car. I don't trust buying a car without knowing what I am getting. I see cars that are below my price range. I know it is a risk to pay for a vehicle cheaper than 3k, heck, even 3k is a risky price. But, I wonder if I go cheaper would it be smarter? Maybe I can invest the extra grand into any car troubles the car may have...Idk, will someone please give me some advice? I need a car asap. I need to have a vehicle by the time I graduate so that I can have transportation for work. I currently live with my mom. I left my job and abusive ex...long story. I am pretty sure I've written about it on here.