I got zero knowledge about programming, illustration. Like many other gamer, we always have some idea which inspired on abc game and hoping some one will invest their money and whoala, this game get famous.
(Not having looked at the target game, but just speaking of game development in general...)
Most people also have no experience in game, UI, or sound design, music, game production, tech or art direction, IT, QA, HR management, etc. Good personnel to fill these needs (and several more, for higher-end titles) should be added to the budget just to facilitate development.
If we hope to do anything more than simply get something made, we'll also need to cover market research, PR, advertizing, distribution, business law, etc.
A handful of acquaintances making something on the side for fun is one thing. But when we turn it into a commercial project in which we hope to pay expenses, and maybe even profit, we have to somehow account for at least all of the above. These are some of the reasons it's tough to arrive at an actual budget.
It's probably much, much cheaper for an established group whose just succeeded on all fronts with a similar title, to make a given game than it would be for a business speculator to put together the same project from scratch to get the same result. Figures based on the former are likely to woefully underestimate the latter, in both time and expense.
This is one of the reasons it's tough to get savvy investors interested.