If you insist on wearing a drysuit be prepared to get hot. They're pretty wind resistant too so bombing around at high speed won't help to cool you off. You can get breathable ones but these start at around £180 for anything decent in my opinion. I have the Gul Solent but I never use it for buggying, too good to get messed up by sand and OBE's! Gul also do an all-in-one fleece undersuit (£30) that wicks away moisture but to be honest you'll be sweating so much your expensive breathable drysuit won't be able to expel the excess and you'll be soaking in an hour.
I have a specific buggy suit that was made by Cunning Stunts before they folded. Waterproof, breathable and all-in-one, nice cosy fleece lined neck as well. Sadly, they're no longer available.