As with almost any business, I would assume that most of their costs are due to salaries and insurance.

However, if you are seeking lower-cost tours, I would recommend any of the various state tours such as Bike Virginia, Cycle NC, BRAG, GOBA, TRIRI, etc. Most of these tours cost in the range of $350-500/week (at least the ones I have ridden on). The fee covers SAG support, cue sheets and/or maps, food stations, camping spaces, luggage transfer, and sometimes meals and special events such as live concerts. I've never considered the fees to be unreasonable for these sorts of tours, and I've ridden a bunch of them in NC, GA, VA, OH, IN, WI.