usa tour.

ok guys as I see a lot of you guys are from usa, well me and the girlfriend we are in the uk by the way , are thinking of doing a usa tour so I was interested in any advice on bike hire etc , I don't want to rent a Harley or cruiser type thing I just don't like them , im looking more for a big adventure style like a bmw gs or similar , is it worth hiring a bike or would it be cheaper to buy one there then sell it, ive seen hire for about $4000 for 28 days , any advice welcome.