As stated the used market (eBay for sure) is saturated with square taper cranks of all types. You can even get campy carbon in ST, and for a rather doable price. There's not much to be gained from a different BB type but weight savings, provided your cranks are good quality. I built my salsa with an older shimano crankset because I had it available and the silver color looks proper on a steel bike. It weighs more than the carbon crank on my go fast bike, but doesn't feel detrimentally softer. Do some looking, or hit up a well established LBS that's likely to have a bin of take off parts.