Depends on what you mean by "optimistic that this will work."

I mean buying in at the $65 for a week level.

That doesn't have to be because he assigns a high probability to it having positive value, it could be because he assigns a moderate probability to it having moderately high positive value or because he assigns a low probability to it having extremely high positive value, etc.

I'm trying to understand the "moderate probability" part. EY's been on so many non-working diets; this is evidence against a dietary solution working, unless there's a reason why Soylent isn't in that reference class.

When computing the expected value, keep in mind that Soylent displaces other food, so the actual cost (assuming the project meets its funding goals) is not $65 but $65 minus however much Eliezer would otherwise have spent on food in a week.

Obviously.