I'm not gonna assume the prices for a PTR in a Mass dealer are more expensive, but in my experience i've found it's still cheaper to buy out of state and have the dealer Massify it before they transfer it, Mass dealers have a tendency to jack up the price before it even arrives at their dealer, then tack on Mass sales tax.
Again, these dealers that sell PTR's in Mass might have great prices, but i'd shop online first to see what makes sense.
Just looked at those Atlantic PTR prices, and i'd bet those are nearly impossible to beat, some have free shipping attached to them. Make some calls around Mass, but i'd venture to say you might save a couple hundred bucks buying from Atlantic.
That PTR PDW with a stock and a tax stamp would be BADASS!! hmmm??