I picked up a set last year from a guy for $180. It was two communicators plus two of the passenger plug-ins, it was missing one set of headphones of the four. I have yet to try them, I am guessing I will have to update batteries, but I figured it was worth the gamble at that price.
My advice...Get a set of Motorola walkie talkies..GMRS..upto 16mile range(or more)...and do a google on "Throat Mics"...they are military grade that hook directly up to yer throat (voice box) and keep the other noises out...obviously a set or a single earphone plug can go into yer ear...
Now I can't say fer sure how they work but I'll be getting a set shortly for the hunting season...there used to be a website that specifically mentioned them for snowmobiling awhile back (3years) and featured on "snowmobile television" and they worked pretty good...Also thinking of upgrading to a set of Garmin Rhinos aswell and they support them too...
The beauty is you still have a walkie talkie for summer use and this can transfer to any motorized vehicle situation...