What are some of the cheapest performance upgrades we can do to the 107?

 

Probably the cheapest would be a K&N air filter.

Next step I think would be Fullsac Cores in the stock slip ons. But combining that with the air filter you might be too lean and require a Street Tuner.

Drilling out the cat is basically free, but I don't know if that adds performance, M8s are very exhaust sensitive.

 

Aftermarket stage 2 is about the best bang for the buck, cheapest performance upgrade you can do IMO. That is if you're not worried about a warranty. Screamin Eagle stage kits offer good gains, but are more costly and not as much gain as aftermarket. But they are warranty friendly.

For my aftermarket work, I think I was all in for about 2 grand including a full dyno, cam, lifters, lifter cuffs headers, pushrods and tuner.