Ruger MKIII. Sadly enough I'm only half kidding.
OK listen up cuz this is the last time I'm going to type this... At least until the next time...
A frame is NOT a firearm in MA. If you have family or friends in a free state they can buy any off list gun for less than you would pay here. Then have them ship the frame only to a FFL. Which they CAN transfer to you since it is NOT a firearm. Then they can just mail you the other parts since they are not regulated items.
Or you could just buy the parts online and have them shipped to you, obviously the frame still has to go through a FFL. I know several people who have built gen 4 glocks this way and all together they paid $50-100 more than they would have in a free state and have a BNIB glock instead of some waaaaaay over priced used gun. BTW I used glock as an example but it applies to all HGs.