Lou's Custom Exhaust does good work and isn't too expensive and has a bunch of locations, Boston, Medford, Waltham etc
CYBA in the vendor section also has nice tips for sale!
2008 E93 335i, MHD, HPF IC, Injen Intake, AR DPs, Alpina TCU Flash
2016 X5 M-sport 35i JB Stage 1
2013 Mercedes C63 AMG, ROW airboxes, power pipe, Eurocharged V6 Flame tune 540 HP