a quick scout of airlines and ferry companies leads me to the conclusion
fly rent (4people) 800(flights) 600 (car) for a grand total of 350/head
ferry (4 people) 1000-1200 (ferry) plus extra fuel/tolls for around a total of 1400 or 350/head (lots of additional travel time though +plus restricted dates for long haul ferry services)
now you could get lucky on the flights (i saw one that was about 140/head) but don't count on it.
this was looking at preliminary dates sat 7th jun - sat/sun 21/22nd jun
expect another 100/head fuel and tolls
100/head camping fees
350/head eat drink spending cash...
for a grand total of around of around 900 bills (budget a grand for safety)
these are very conservative numbers. people have been known to get away with it for a lot less...

but with the change in prices re inflation/fuel costs/flight costs where we used to look at doing it for 750ish in 2004, things have gotten more expensive...
chemicallio