Sam, some things about your post confuse me, but then again I am easily confused.
You say you have a 7m+ Lencraft, and if you are even reasonably experienced with it, you already should know the answer to your question.
If you are not experienced then you are likely to have trouble raising any money as donors would like some expectation that you will actually complete the circuit.
Why do it for charity anyway? Are you just looking for someone to pay for your boating?
I did it in 2009, but then again I already had my own boat, an excellent crew and in no hurry-so my costs are immaterial to your cause.