As far as local area stores. I grew up in Salem, Ma (now in Methuen) and PJ's on Route 1 has decent priced dry goods. They have a HUGE selection of freshwater but only one row of sw
livestock. They can pretty much order anything you want though and they shouldn't be too pricey. They're probably the closest to you.
If you ever get the chance, hike out to Tropic Isle in Framingham. HUUUUGE selection of fish. A little pricey, but its worth the trip to see their selection. Their website is www.tropicisleaquarium.com
My recommendation, although its a bit of a drive if you live in Boston, is Aqua Addicts in Salem, NH. It's right over the NH border. Small store - but, its dedicated to just saltwater and reef aquariums. Very specialized, very knowledgable, really great prices. You can go to aquaaddicts.com and sign up for their weekly emails - they'll email you every Tues or Wed with a list of new arrivals with size and price. Really classy group of people work there.
There is also a place on route 28 in Salem, NH called SeaWorld. They have a really nice selection of sw
fish, but very high priced. Their medium sized Zebra Moray was $150 - AquaAddicts, around the corner, had one for $80.
Basically, if you are going to buy an expensive and/or delicate fish or need a big clean-up crew (their clean-up package for a 55gal would be $60) - check out AquaAddicts in Salem, NH. Its a small store but prices and knowledge is well worth the trip. Save on taxes too.
Sorry for the long post.