I'm looking for a ballpark figure of how much it costs for headers to be sandblasted.

Cost me $25 to have the headers and y-pipe media blasted. Not bad. They came back clean and held the hi-temp VHT paint very nicely.

$20 if I did it, but you're nowhere near me.

shall I stop by on the way to the TA Nats in ohio?

Well if it's not too much out of your way and if I'm not working that day then sure. I'm east of Indy. If you wanted you could drop them off on your way to nationals and then pick them up on the way back, that way I wouldn't have to try and get off work. Just something to think about. Let me know what you decide.