You could be looking at anything from a maladjusted or broken selector, to a transmission with low fluid level or even a transmission that has pretty much failed internally. All three possibilities can see a car with reverse and no other gears.

A transmission specialist is your first port of call, once you’ve checked the transmission fluid level yourself, of course. The owner’s manual will tell you how to do this.

With a limited budget like yours I would suggest to go for a car with a good reliability record. While the Mercedes-Benz is a good car you are likely to be facing an expensive repair if anything should go wrong. Consider a Mitsubishi 380 or a Toyota Camry of around 2000-2003.

Try beveling them again and see if that makes a difference. That usually fixes the problem, but if it doesn't work consult a brake specialist and perhaps try another brand of pad.