My prusa i3, have had its parts printed with the printers at my work and its still not finished yet. Turth to be said, it's probably much better if you buy a complete kit. The 8mm rod can be expansive if you live in the US, and the leadscrew too. Alternatively you can go with imperial use 5/16 rod and rod, but keep in mind you have to adjust the design in consequence.

So far I have spent about 300$ on my prusa and it's halfway done. The board can be expansive or cheap depending on what you buy, it can range from 40 to 180$ US. The 5 motors alone add another 100$. Metric screw, bearing, shaft, leadscrew, coupler, belt, hotend, power supply adds another 100-200$. Keep in mind that I have cut the frame myself with the laser cutter, that save another 30-50$.

At this point, I would advise you to buy a new kit.