Just jumped into the Tanfo world, originally planned to use a .40 Stock3 and grab a 9mm conversion kit for production. Like you, was shocked on the conversion upper cost from EAA and had to adjust my plan with a complete separate pistol.
.40 Stock3 setup with SAO with PatriotDefense goodies: 14lb hammer spring, optimized trigger, firing pin, and sear springs, BOLO, Henning XL firing pin, removed firing pin block, Titan hammer, Dawson fiber optic front sight, Xtreme trigger and conefit guide rod, EGD grips and mag well. Henning 140mm mags from BSPS.
No thumb rest now, but might drill/tap the frame later on to match the Limited guns. Someone did offer a thumb rest that replaced the slide stop, no permanent modifications and deleted the slide stop which isn't a bad deal for Limited.
https://www.speedshooter.com/product_detail.cfm?id=NF17-4 TF&n=Shooting-Sport-Tanfoglio-CZ-Slide-Lock-Thumb-Rest