I run rugged radios in my race buggy. They are really nice but VERY expensive! If you need JUST A CABLE expect to pay about $50 for that 1 cable. There are a few options out there but a lot of it depends on your budget and how nice you want it. First off is everyone wearing helmets? Or will headphones be used? Or a mix of both? Rugged Radio head sets start around $100 per set and go up from there. If wireless is needed and everyone is wearing helmets then there are plenty of offerings from a company called Sena that have been around for many years and make a great product. These also start around $100 each and attach to a helmet. There are cheaper offering out there on Ebay and other places. You will get mixed reviews on them and honestly you get what you pay for in this market. If you want hassle free go with Rugged Radio. If you can live with the daily problems you will end up encountering then there are cheaper brands. Also with the Rugged Radio set ups you can pipe music through it via bluetooth or 3.5mm jack if you so desire.
I also STRONGLY suggest you go with a PTT (Push To Talk) set up because otherwise you will hear every squeak, giggle and groan from every person and it can get real annoying real fast. Also you will always have that one person who is breathing right on the mic and you can hear it constantly. In the race buggy we dont run PTT though because I need to hear my navigator NOW and we are in constant communication back and forth so it is quite a different scenario.