4mil is a Aftermarket crank usually made by Hot Rods which is 4 millimeters over the standard stroke. With your budget i would throw a 4mil in there and port it. A 4mil crank will run you around 465 for one. You can call up Jeff from FAST the 4mil page is HERE if your handy you should be able it drop it in yourself if your not confident jeff can do it. I would get a4 mil and port the cylinder. Youll never look back again. Again thats the expensive route the other way to go would be Port the cylinders for your riding style for now and do a 4mil later on.