I second Dazed comments on the 71s. It was only certain tracks but it was painfull to listen to. For most tracks they are fairly good and the bass is the most I've heard from in-ears (not that detailed but plenty of it ).

I'm now using Shure E1's and they are just fantastic but fairly over your budget.

I still use the 71's when festing and general roughing it. I've read a lot of -ve stuff on the B&O's but that's usually comparing to Etys and Shures which are double what you've found the B&Os for.