What I'm driving at is that some ideas you can do a minimum viable product very quickly, other more ambitious ones might need months of work - I was trying to avoid making assumptions about what this unknown idea might be, and throw the focus on potential cost to launch. The question is so open-ended that it sounds like an interesting idea without any financials yet; so I'm trying to estimate the cost of satisfying my curiosity about whether or not a market exists for whatever-it-is.

A webapp that solves a particular problem by matching buyers and sellers might need only a week of work to begin being useful. But not all ideas are so straightforward - for all I know s/he might be imagining the next evolution of the spreadsheet.