How about a long weekend/week (ish) ride stopping at varius places along the way. I could'nt warrant 3 weeks. I normally work for myself and have family commitments. I do miss the weeks away on the bike though.
My suggestion would be a visit to the 24 hours endurance at Le mans - Great roads, not too far, european riding for those who haven't done that yet, free camping, 24 hours of bike racing (+ loads of other things). Quite cheap. petrol, food/drink, cheap ferry and if people share circuit tickets not much to get in. I didn't bother buying a ticket the last few times I have been there and just borrowed a ticket for a wander inside the circuit every now and again. It is a great atmosphere and much cheaper than the TT. haven't been for a while but you could also have fires, they even supplied the firewood!!!