the ex85's and ex90's sound virtually identical, and i mean so close you'd have to have both pairs in front of you to tell the difference. ex85's are absolutely billy bargains and the best buy under £100 imo.
Theres a modding thread of mine on this site and also headfi. The 90's do sound a tiny bit better - I think the only reason for this is that the 90's have foam in the ear channel and the 85's just have a paper cover. One thing to note the 90's are a bit heavier!
Just had a browse on some famous auction site to see there only 19.99 with £8 postage. Does that sound right?