Just my 2 cents, but, I would advise caution against just replacing parts without an accurate diagnosis of the exact cause of the problem Ö
Take it to Lloydz, Kevin X, or The Vic Shop.. get an accurate diagnosis, prognosis, and repair/replacement... save money, worry, time..
Cutting the stock airbox out and replacing with an estimated $150 replacement?? This sent a RED FLAG. I don't think they can find any after market airbox for $150 (maybe used S&S)