I just looked up the crane cams, they are pretty much a stock replacement, if you wanted a high performance cam you have to get the competition cams, which will boost some power, but you also will need to get a tune to allocate the appropriate A/F ratios for the different lift on the cams.
its going to be more then $350 to make it reliable and worth your while, do little mods here and there if you want more power, zorrex said a UDP would be a good idea; hes right... Also look into a header, and deleting the EGR system (also will require a tune).
Seriously modding to get lots of power is more pricey then $50 here and there. Its a domino effect, every action has an opposite reaction. If a lot more power for low cost is what you want, sell your Mystique and buy an SE sport contour, or an SVT (they are getting that cheap). Your mystique is nice and clean, and fairly low mileage; you probably could get in the 2 grand region for it, around here I see low mileage 98+ SE sport contours with 5 speeds going for $2K. (Obviously this is the easy way out).