That sounds about right to me, but don't be afraid to ask around different places - you will get different offers.
I recently got trade in prices from 4 BMW dealers for my E90 and they varied wildy - by over £2.5k from best to worst offer.
2012 Alpine White E92 335d M Sport LCI | Coral Red Dakota Leather | Media Package - BMW Professional | 313 Wheels | Evolved |
Previously - 2009 Alpine White 325d M Sport LCI | Auto + Paddles | Media Package - BMW Professional | BMW Performance Front, Sideskirts and 313P Wheels | Black Grilles |
Carbon Black E46 ///M3 '04 | Manual | Evolved |