Using the information from Racecar engineering, you could build a pretty good system for your current motor for pretty cheap. I don't have the article in front of me, but it has a lot to do with where you put the transitions (i.e. 2 into 1 collectors, etc) and the volume of gas exhausted from the motor. It is worth the read and the time to build the spreadsheet and figure it out (imho, anyway). It will also help with selecting off the shelf components because you'll understand the advantages and disadvantages of each design.