Ken, it's difficult to gauge because I also tied in a trip to London and stayed with my folks and used the last of my frequent flyer miles....
...but I can tell you this, based on CURRENT conversion rates:
1 week ticket pass to MC: 110 Euro ($150 US)
roundtrip flight to LJU from London Stanstead: 60 pounds ($120 USD)
food + drink for the week: $400 each (?)
SUB-TOTAL 1: $670-$700
roundtrip flight from NY/tri-state/Boston to LHR: $900 average
*
this really is the biggest variable since folks are coming from all over
SUB-TOTAL 2: $1600
hotel: approx 50 Euro per night per room ($70 USD or $350 total)
rental car: approx 30 Euro per day (compact car) ($40 USD or $280 total) + gas
Each hotel room would be split across 2 people. The car would be split between 4 people for at least 7 days.
SUB-TOTAL 3: $1850
For those camping, go with SUB-TOTAL 2. Good luck carrying a tent and all that shit to the wilderness of east europe.
For those who like bed mattresses, showers, cups of coffee, and a hot breakfast, go with SUB-TOTAL 3.
So all in all, think about setting aside $2K and you should be good to go.