Speculate on commercial property prices online?

Are there any fairly direct ways to get exposure to US commercial property prices using an online broker (other than REITs)?

I plan to do a lot more research before I do anything, I’m just trying to understand the lay of the land. And of course I don’t intend to invest any money that I’m not ready to lose. (Also worth noting when it comes to these kinds of things: I don’t intend to make any investment that doesn’t have a maximum possible loss < the amount of cash I hold. Silly maybe, but there you go.)

(The way I’m reading it, there are a few residential real estate-related indices but no commercial real estate-related indices.)