What will it take to get me and my mods in 300 HP?

B18 head with a Skunk2 intake... oh wait this is a mustang site, still?

The cheapest route, I guess, would be some aftermarket heads and a tune. Or just dump a supercharger kit in there...
 
You will need some heads. AFR165 or TFS heads would be the best way to go. Port the lower on your cobra intake and get a TFS stage 1 for an off the shelf cam or a custom one. You should be able to get by on the 19lbs injectors but I do suggest some 24s. 70-75mm throttle body, a 190lph or more fuel pump and you should be good. This all depends on what condition your shortblock is too...
Kevin