I wouldn't take less than 750, you can't build one for less unless its low quality. And you did the break-in, hell whats a thousand rounds cost? And they don't start shootin good till then.
there are 3 vendors that forge lowers and 4 that forge uppers so no matter which final name is on the parts it's one of the 7 vendors. all of the parts are all the same with the exception of finish and logo. so if i build an ar with a 135.00 RRA lower all i get for the extra money is a logo. if i build it with an essential arms 89.00 lower i don't get the logo. so you have to decide if the logo is worth the extra bucks. an ar built with a bushmaster lower or upper is no better than any of the others. an off brand ar be it an m-4 or a A2 is worth about 50.00 less than a name brand ar of the type.