Don’t do it. I got one just to use to ride to the train station ( about 5K’s each way) so that I could lock it up, leave it and not be bothered if someone wanted to vandalize it . No one ever did. However, it was never ridden hard and only on roads and pavements and started for fall apart almost immediately. Gave it away after 9 months as it would have cost more to fix than to buy another one.
Got a solid single speed in the end with one front break and nothing worth stealing off it. Worked fine.
Advise is to buy a good secondhand one in the mid range like a Trek , Giant or specialized for $ 200- 300. If serviced regularly they will last for ages. I have abused my Giant for four years and never a problem other than normal wear and tear.