Don't forget that only a portion of the maker's time is spent making guitars. You can't just calculate $1000 for materials plus 100 hours of labour x $20/h = $3000 for the guitar.
There's overhead costs, heat, electricity, business permits, downtime due to shortage of order intake, marketing time, marketing costs, time spent procuring and picking up materials, rejected materials, mistakes, warranty costs, inventory costs, tools, consumables, taxes, insurance, bookkeeping, employment insurance, worker's compensation, vacation time, time spent communicating with client, computer costs, internet costs, and clients who don't pay their bills, shipping damage, etc......"100 hours to make a guitar" does not include the other 100 hours of time required to do all this other stuff.
In the "consulting" world, where a company's income is based on selling manhours not products, we have to charge 2.5 to 3.5 times a person's salary to make a small profit assuming a reasonable size organization of 20-30 people and about 80% employee utilization. Larger and smaller companies often have higher overhead. The 2.5 to 3.5 multiplier covers overhead costs, downtime, and profit. An employee earning $50/hour needs to be charged out at $125 to $175/hour to make it worthwhile. Similar principles also apply to luthiers.
In the small volume "equipment sales" world, where the company's profits, overhead, and risk costs are buried into the equipment price, we often will consume huge amounts of consulting, technical, and marketing manhours making proposals, bidding, and dealing with clients...but all of those costs are buried in the equipment price (and warranty terms), so that the sales price of the equipment is multiple times the actual cost of production. Thus if it costs us $1000 to make a "guitar" we might have to charge $5000 to cover all of our costs.
Finally, at the end of the day, the client must pay for the costs. If our costs are too high they will purchase elsewhere. In the consulting and equipment sales worlds, this often means the client purchases sub-standard equipment and regrets it later. In the luthier world I imagine that many luthiers are overworking and underpaying themselves; something that would cause a normal corporation to go bankrupt.