

For me, my favorites are:
RAH-66 Comanche for flying sim.
Wolfpack (from Brøderbund) for submarine sim. I believe it is also free on archive.org. (Added link: https://archive.org/details/msdos_WolfPack_1990)
Euro Truck Simulator 2 for trucking sim.
F1 2019 for racing sim. But it pretty much requires a wheel and pedals if you want to get really good, which does add to the cost.
EDIT: added link
https://archive.org/details/msdos_WolfPack_1990
Have fun!