You'd need some spacers but yeah get the cheapest bsa 30 bb you can basically and the mtb spider or a direct mount ring
DJ is selling some Hollowgram Si arms they are the sweetspot for mtb I think. Not so spendy that you are sad when you mash them but nice enough to be smug :)
Hmm, so would presumably I could just buy their own (much cheaper) BB instead?
http://www.wiggle.co.uk/race-face-bsa-cinch-30mm-bottom-bracket/
and heir axle get some arms and away it go?