Best Place to Invest While Saving for a Car

Hello, long-time lurker first-time poster here. Perusing reddit late at night like I usually do before going to bed, I came across a post that had a great idea in it. Rather than taking out a 5-year car loan when you want a new car, instead, with a little patience thrown in, reverse the equation and start putting that monthly payment away, and buy that car in 5 years.

I've decided to start that process in order to get a car I've wanted for a long time (BMW M3 in case anyone was wondering), and I figured rather than put the money into a savings account or something, I should invest it instead so it grows.

Question is, where is the best place to invest it where it will be relatively safe? I'm not quite looking for government bonds, but something sort of in the low-mid risk area, like a conservative ETF or mutual fund, to stash away monthly payments until I've saved up enough to pay cash for the car.

Any suggestions?