Here is what I came up with.
For example:
1. Upper with handle
https://www.primaryarms.com/Radical...z1aQ.Eis5.AreXPg..A3iSLA.b..l.BStr.n...VaCBNw
$240
$12 for basic charging handle
2. Bolt carrier group $80
http://www.surplusammo.com/saa-m16-complete-bolt-carrier-group-mpi-tested-223-5-56/
3. Complete lower $190
http://palmettostatearmory.com/inde...wer-magpul-str-edition-black-no-magazine.html
They have complete lowers as cheap as $149.
Total $522
The rest of the money will be spent on MA compliant muzzle device, pin and weld, bringing it up to $600.
You really can't get good optics under $200 - waste of money, IMHO, save your $$$ and use iron sights for now.
Edit: with Palmetto State Armory you can get your AR as low as $442 and it will be at least as good as low end S&W.
If you're in MA, palmetto will not ship lower receivers, even stripped ones, to MA FFLs.
Also, don't skimp on the BCG. It is the heart of your rifle. I can't tell very well from the picture, but the gas key staking looks a little anemic.