I don't agree with doc saying he's basically a free agent. I understand the point he is trying to make but the trade wouldn't have been made if either
A: Arte didn't want to pay him beyond this season for the remainder of his contract
B: Arte and Eppler didn't think it was possible he would want more money
I mean, if he comes to the Angels and completely sucks, then it's likely he doesn't opt out. But if he comes over and is even mildly successful (which Arte and Eppler obviously wanted) then there's a good chance he does. The Angels are clearly interested in Upton long term. Otherwise why bother making the trade? It wasn't just for 1 month and slightly increasing the chances of the Angels winning the 2nd wildcard. They obviously felt they could keep him long term, thus filling the huge black hole the team has had in left for the last decade.
And no, a few million isn't a big enough difference to keep them from retaining him. If it is, then they were stupid for making the trade in the first place.