I was wondering what kind of exhause system would be the best for performance and sound at a reasonable cost for a 2010 6.7 cummins??

 

I would leave it stock.

 

If you're talking about a cat-back, I'd just throw a muffler delete pipe in place of the muffler and call it a day.

If you're talking about deleting your DPF/Cat/EGR, I went with an AFE 4" turbo back exhaust and an H&S Egr delete and programmer and I couldn't have been happier. With an S&B intake and the above bits I was running 13 second 1/4 miles and getting close to 20mpg on the highway.