I have a Rock Island 1911 that I converted to 9mm. I don't have a lot invested in the pistol and, more importantly, I don't have an emotional investment. My state doesn't have that quirky Texas requirement, so anyone passing the course can carry anything.
That said, I don't particularly want students bringing their own guns to a class setting. My rule is, if they already have one ... leave it at home, or locked in the car. They shoot mine. In the past, when the NRA Basic Pistol class was only about safety and all that was required was to demonstrate the ability to load and fire one magazine of cylinder without endangering anybody, I would let my students try both the semi-auto and a revolver (either .22LR or .38 Special). Now that the minimum course of fire has been increased to a minimum of 50 rounds, I don't double up any more.
Go 9mm. That gives you the widest assortment of guns across the full price spectrum, and 9mm ammo is less than half the price of .380.