I did an L2P road ride with a group of people off Bikeradar forum in 2010. Similar cost issues had put people off.
Collectively, we paid for minibus hire and a couple of non-cyclists kindly offered to drive our kit in exchange for their trip paid for.
I think there were 18 of us and it cost about £300 each which was for ferry crossing (minibus plus passengers and a load of foot passengers), minibus hire, fuel, hotel rooms on a shared basis (Campanile in calais and Amiens and then a random one in Paris). The minibus brought back a load of people on the way back and the London based ones got on the Eurostar.
Our route was London – Dover, Calais – Amiens, Amiens – Paris.
I’ve provided links to the route in a similar thread if you do a search but it’s about 70 miles, 115 miles and 100 miles.
If I were to do it again, I wouldn’t bother with the support aspect. The riding isn’t hard and modern bikepacking bags make carrying kit easy and it’s basically 3 days of touring. If you pre-book hotels etc you’ll only need to carry the minimum kit for off the bike.