Shadow7874

I have a collapsable Fuji bike ive been using the past couple weeks since my old bike was stolen. Its not a terrible bike but i dont like it very much. Its quite heavy and i really dont need a collapsable bike. I use it to commute to classes but im always jumping curbs and riding off road, plus some of the sidewalks around atlanta are pretty rugged. Id also like to get into mountain biking a little so im hoping to have a kinda all around trail bike i guess. I have been thinking about finding a lighter frame on craigslist or ebay and then swapping everything over but i really dont know what to look for. Id also like front suspension if i can get an ok setup fairly cheap. Ive seen suntour xcr forks for less then $100 new on ebay. Would they be ok for an entry level bike? And im semi interested in disc brakes depending on how much it costs to convert. If i buy a frame that supports both v and disc brakes how much would it cost to add those later?

Basically looking for suggestions as to what to do. Any recommendations would be great. Id like to keep the cost under $300 but any thoughts will help. Oh, and the left crank arm is cross threaded so the pedal wobbles, can i buy just the arm fairly cheap? its not a huge deal but it feels kinda funny.

here is a pic of my bike, if anyone has some info on it that would rock (like what upgrades will fit, mainly a fork)