Your LBS may like the BB30 system, but you need a frame designed for it, if you have a standard (i.e. 68mm english thread) BB shell, unless you cut it of, and weld a new shell into the frame, BB30 is never going to happen for that frame.

Not sure what you are saying about the octalink DA being a lot of money, if your talking about the crank, if you can get one, it will be very expensive, but that it the biggest issue, availability, if you mean the BB, this depends, its a V1 octalink, these can be very hard to source, it it's a V2, the ES25 or ES51's are cheap and readily available.

If your current crank arms are still in good condition, can the rings alone be replaced?