Have a 'day out', and go to Micheldever (just down the A34). I bought my front (Trail Attack) from them last year, and they were about £10 cheaper than anyone, about £87 fitted from memory. They do offer a 'ride in/ride out' service (costs a little more), however, I like to take the wheel out myself, so that I can have a good poke about whilst there.
I've found the receipt, it was £78.28 inc vat and balance. Last October.
fitted was mentioned 
for a set of TKCs, when I actually wanted "a list of approved tyres by BMW" as the manual states one should get from BMW. 

