Uh, you must have an interesting idea of "not too much". The single speed titanium is what, 22 lbs stock. Before you drop 5 pounds off it somehow and at some price, you need to add in weight for some gearing to be more or less equivalent with the other lightweight bikes mentioned. With Brommie, you're capped out at 6 but that probably adds what, at least 2 pounds? So now you've got to go from 24 down to 17 "without spending too much". Seven pound drop cheaply, I don't think so.