Players today should expect to pay between $400 and $550 when shopping for a new custom fit professional grade driver. Unfortunately what often happens is they pay nearly twice this amount because of what's called upselling. The fitter says "Based on the results of your fitting the shaft you need is on our custom tier and will cost an additional $300." You end up paying $700 to $850 for a driver. At most club fitting chain stores the staff is trained to upsell the customer to increase their commissions and profits.
Is paying an additional $300 for a custom shaft worth it for most players? If you are a PGA Tour Player the difference may be worth it ( they don't pay for their clubs ) but for most amateurs - even scratch players - the difference is small if any.
Most recognized golf club companies will offer 3 to 4 shaft options at no upcharge. These are high quality shafts from reputable companies such as Fujikura, UST Mayima, Aldila and Project X.
The most important thing is to be professionally fit to find the right shaft for your swing characteristics.
If you really want to improve your game take the $300 you saved and purchase some lessons from your local PGA Professional.