I do two trip's a year. Of the type you are talking about. How do I do it? Well first off I'm retired. Second I live on my own and have a nice lady friend who looks after my house and cat's while I'm away. So that's the time sorted out. So I suppose it's the money. I have an allotment so I grow a lot of my own food. I have a wood burner. And I get a lot of my wood in palates. Which I cut up and store to heat my place up. I collect rain water and re use that after being filtered, Washing and toilet. The only main water I use is in cooking and drinking. I fix most of the stuff broken. Don't believe in the bin it and buy new. I do all my servicing on both my bike's and my car. So what do I have to pay. Local tax's, electric, and a few other bit's and piece's. As my house is paid for I don't have a mortgage or pay rent. So all the money that come in the fount door is my own. I have more coming in than I need, So I can save quite a bit. That is used to go on the trip's of a month or more. You can rent a small self catering place for two week's for less than it will cost to camp in different site's each day. So make you way to where you want to go. Rent a place stay two week's and then ride back. This way a lot of what you need to pay out, you can settle in the UK. I.E. Crossing ticket. Accommodation paid up front. So all you are looking for is food and petrol. If there is two of you a lot of the coat can be shared. so that's half as much.
Hope that helps.