Went a couple of years ago with a couple of others and had a brill weekend. Sailed over Friday night from Hull, go to the Ring Sat lunchtime. Did a few laps Sat pm, some more Sun am and came back overnight Sunday. 
  
Lovely place to visit even if you don't want to drive the 'ring - great scenery and some impressive machines always there. 
  
Only boring bit is the drive from the ferry port to the ring and back; quickest way is not the most impressive visually, but it's only a few hours steady drive.  
  
Can't remember costs, but the hotel wasn't stupidly expensive, ferry was reasonable and I didn't use that much petrol (about three tanks all told I think). 
  
I'd definitely be up for another visit at some point. For general info on the ring, check out http://www.nurburgring.org.uk/