one needs to compare apples. The top teams (Ineos/JV/UAE) are all about 50M€ per annum., so over 4 year cycle about 10 times your quote for Charal.Average budget of a TdF team : 18M€ per year. Some teams are way above that.
Estimated budget of the best-funded IMOCA campaign 2016-2020 (Charal, by far) : 15 to 20 M€ over the whole 4 years cycle.
So no, there is still a large margin before saying TdF costs less !
But regarding bang for the buck, the jury is out. I guess is depends on what you're trying to achieve as a sponsor. For example, the TdF's international media coverage is undoubtedly orders of magnitude higher than that of any sailing competition, Vendee Globe included.
But it doesn't convey the same image...
Totally different market, guess another upside for VG is you sell a boat once you're done too. Cycling the team has very few actual assets.