MAF-T's are under $200 new and are the cheapest easiest way to tune it yourself. They are limited though as they only increase/decrease by percentages and really are just tricking the PCM. LMK if you want to try mine out, its been sitting in my garage for 3 years. It sounds like your issue now is the cam + non-calibrated maf, as in you fixed all the codes? Have you tried Vengeance? Is your car an A4 or M6? 13mpg is bad but in an A4 in the city you'll only get about 15-17 with those mods. I usually get 16 city and 23-24hwy, M6 with 400+hp.