After the thatcher rabate and the eu subsidies GB pays around 18 million pounds per day to the eu.

If we divide that through the 50 millions brits it makes ~0,36 pounds per day  or 131,4 pounds per year for every brit and this would place GB on place 8 of the 10 net contributors.

What a high price for a domestic market of ~340 million people and freedom of travel, living and working where you want.

The funny thing:

Of course GB can get out, but they would have to negotiate all treaties again and as net effect they would have a status like the scadinavian countries:
They are part of the EU just without power to say anything.