I would like to buy the rifle it's on and trade it to someone behind the lines. Would it be worth a post ban Colt lower?

Assuming you are talking about a preban Essential Arms (not eagle arms) cast lower, I would say it's not worth more than $300 complete in excellent condition.  You could probably get a little more from someone who isn't aware of the cast problems,though.  I'm not sure what type of postban Colt lower you mean but I would guess around $400-425 complete in ex cond.  If it's a preban eagle arms complete lower then it's worth around $400-450. IM me if it's Eagle Arms.

Talking with the owner of Essential Arms, he never had any "cast problems" with his investment cast lowers.  Also, in all of the years I have been playing with AR-15's, I have never seen a broken EA lower, nor have I talked to anyone who has.  I have never seen any other problems with these lowers.  I know a number of LEO's with AR's built on EA lowers, all without problems.  I know of full autos built on EA lowers, owned by Sheriff Offices, that all work just fine.  So much for EA's cast problems.

Yeah, I've never heard about any problems specifically with EA either but there are plenty of horror stories out there regarding cast lowers.  That doesn't mean preban EA cast lowers are worth as much as preban forged lowers, though.  Facts are facts and it's a fact that forged aluminum is stronger than cast and less prone to breakage, whether people have had problems with EA or not. Cast lowers are not worth as much because they are cheaper to produce than forged and the demand is less because most people would rather have a forged lower, just for peace of mind.  Personally, if I had to have a cast lower, I would go with EA over the other options but I wouldn't buy any cast lower with the preban price tag.