I'm going off of the top of my head here, so I may forget something...but here is the basic breakdown of what you need to make a RZR street legal.
-Turn signals
-horn
-safety glass windshield w/wiper
-Rear view mirror
-High/Low beams w/indicator
-DOT tires (there are a TON of different 14" wheels on the market for most side x sides, so you can get any light truck tire in 14" and they will work.)
-license plate w/lights
-registration and insurance
to get the license plate and registration, you need to have everything else that I mentioned, and then get a TR-54 form from the SOS and have an officer do the inspection, and sign off on it. Bring the signed form back to the SOS and they will issue you a new title stating it is an assembled vehicle instead of for offroad use only, which will allow you to plate it.
There is a company called bull dog ATV that makes a "street legal kit", which gives you all of the electrical components that you need to make it legal. You can piece the kit together yourself from autozone or any other auto supply store, but the bull dog kit is easy enough. The windshield is the most expensive part, there are pre-made ones online..but they are ridiculously expensive. Your best bet is to have one made at a auto glass shop, and then fab up some type of frame for it. Or you could just use one of the plexi-glass ones on the market, which cost less that $100 and hope the officer doesn't notice

, same with the DOT tires. But like I said, cheap light truck tires work good enough...and if you buy used, you can do it for next to nothing.
Monroe Motorsports does "street legal" RZR's, but they jack the price WAY up, you can do it yourself for half of the price.
then i guess you throw on the dots.Have them sign off and then do the'' switch-a-roo"
I saw quite a few RZR's pull into the dunes last year (plated) with the factory tires still on them, so either there are a lot of "switch-a-roos" going on, or there is an officer who turns a blind eye on that point.