Whatever you do, don't bring your business to the Powder Horn in Hyannis. They are the most rude people I've ever dealt with. Four Seasons in Worburn is where I do my business. He's very kind and has very good prices.
Also, I haven't bought a firearm from them yet..I've heard their good but AG Guns in Lowell actually advertises under new guns a Law Enforcement section that shows the discounts on selected guns..They are good deals....Good Luck!!!!
I bought a Glock 27 (and extra LE hi-cap mag) a few years ago from Law Enforcement Equipment, Inc. 781.894.2879. His prices and seletion were very fair, total time in the store - just over 30 minutes (figuring out the federal form). They are in Waltham.