how to convert my 21 speed mountain bike into a road/cycling bike? I was wondering if I could convert this https://sphotos-a.xx.fbcdn.net/hphotos-ash4/q71/s480x480/430156_461794267240029_1042500253_n.jpg to a cycling bike like what would i have to do to that bike to convert it ? tell where and what and how much the parts are i want it so i can have better cardio and endurance i live on gravel road but i can get to pavment from my house. i dont hav any money to spend on a new one so i was just wondering if i could do tires and pedals and maybe bars if it all come less then $100 iwas hoping to sped around $70 or less*** i race motocross and saving for racing so that is why i want the cheapest way lol ih and i dont have any cycling shoes i was just going to use regular training work out shoes.. so if u guys could help me out give me websites and  prices and everything that would be great
Start with your tyres. Go for slicks, the narrower the better. I used to run 1 1/4" tyres on my old mountain bike, at the time this was pretty much the lower limit on a 26" tyre. This will be by far the biggest bang for your buck. 

It will probably also blow your $70 budget if you get good tyres. You may also need to invest in new tubes, depending on what you have currently. But it will make a big difference.

The other thing that springs to mind is to improve your position. Difficult to do this much given the geometry of the frame, although I have heard of people putting aero bars onto their MTBs. Should improve things but its more cost. 

As for pedals - remember you'll need shoes as well - and these on their own will probably blow your budget. I'd stick with what you've got for now and think about upgrading as and when you have the cash.