I would be very weary of a clubfitter upcharging you for a shaft and not explaining their reasoning or why that shaft will outperform the stock option. The AMT Red is considered "stock" for T300's, but there are a number of non-upcharge shafts available through titleist that covers a wide range of trajectories/weight etc. At the very least they should explain why they recommend a shaft as well as getting your feedback and agreement in that shaft.

I was fitted for a set of irons last year by a Titleist club fitter, the KBS Tour shaft was the one that came out on top for me, it improved the dispersion of my shots considerably, there was no upcharge for those shafts even if there was it would be a worthy investment.

My fitter worked with me for about an hour and we tried a number of shafts including up-charges. The numbers favored the T300 with the AMT Red R300 shafts for maximum performance. Also tried the T100 and 200 heads.
Needed a nap after the fitting. My guy knows his stuff. Accuracy and distance was out goal and we got what we were looking for. There is a shaft for everyone and some require an upgrade. With respect.

I have worked with this fitter for years and respect him. He has been a Product Specialist with Titleist for a number of years. I had two fittings booked. One for irons and one for the new drivers. He fitted me for my 917D2 when they first came out and we did not upgrade to the TS series, based on the numbers and trying various shafts and heads.