Porting = Making your intake port & Exhaust port(??) on you motor bigger by boring it out. The more you bore out the more aggressive your motor will be.
Polishing = What is sounds like they will polish up your intake so that there are no little places to cause air drag. You have to think about the fact that there is a lot of air and fuel going into your motor when you hit the gas. by polishing the intake on the motor you are allowing the air to flow with out any restrictsions.
As for cost on this I couldn't tell you. Mybe scott can anwser this.
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