I normally do a long weekend, which consists of a cheap-ish 8am ferry (£16-£35 each way Dover-Dunkerque) on the Friday so that there's no rush getting there, a day touring the region on the Saturday (if the 'Ring isn't open), then a full day at the 'Ring (which can be 4-20 laps depending on closures), and then home on the 2pm ferry on the Monday or Tuesday (depending on 'Ring opening days).
Probably use 2 tanks there, 2 tanks back, 2 tanks on a full day at the ring, and 2 tanks per touring day - so a total of about 8 tankfuls or about £500.
Probably use 2 tanks there, 2 tanks back, 2 tanks on a full day at the ring, and 2 tanks per touring day - so a total of about 8 tankfuls or about £500.