IMO, the “experience” isn’t worth the time, especially for your fairly rushed agenda. I think the “experience” of Eurostar is a better expenditure. Are you taking a car? The ferry is usually relatively cheap for foot passengers, although going to Jersey, etc. may make it more expensive.

Where are you finding the prices???

My hatred for boats of any kind is well documented, but I would Strongly Discourage taking a ferry. If you’ve never been on a boat for very long, you probably don’t know how you’ll react. If you’re like me and 97% of other people, you’ll be seasick and it will be a miserable few hours. The shortest ferry across the channel (I think at Dover-Calais) only takes an hour and a half, but then there is the actual getting to and from Dover and Calais, as most people don’t want to spend much time in these places. (it’s a good hour or more to London and Paris, respectively, by train)