I guess they would have had to replace the bottom bracket with one with a shorter spindle, but so what, that's not $150 by even the wildest stretch of the imagination (unless they are putting in a Phil Wood sealed bearing BB or one of those Gucci Campagnolo ones with the titanium spindle & ceramic bearings). A Shimano LX cartridge BB costs $25 or $30, and I doubt they would have gone nearly that high on the food chain.
I asked the guy today what it would cost for them to replace my triple crank for a single if I provided the crank and it was like $150. No thanks, I'll watch a couple of YouTube videos and spend $60 on the crank and do it myself. Yet another reason to ditch every thing on the bike except for a front brake.