I'm new to mountain biking and just bought an old trek 820 antelope for $70 bucks. Not knowing the first thing about bikes, I didn't realize that the bike has no suspension and apparently one of the gear shifters is not working (the one that goes from 1-7). My question is, should I invest in a suspension fork and new gears, possibly even new brakes, or should I buy a new bike (I'm considering the Trek mountain hardtail 820)? I will be using it around the city but also on some rocky trails. My budget is around $300.