First off, you are talking two different actions and levels of quality. Can't begin to address the differences. If you are saying that he wants your 870 and $200.00 for his 11-87 and his is in equal condition or better, then it could be a good deal. Might ask if you have a use for the 11-87 and do you really want one. Both of these shotguns are very serviceable and give good performance. I guess it comes down to a matter of need. I cannot say anything bad about either but as I said before; Two different animals.
Be Safe !!!