So really, what you'll be doing is creating a new game from scratch using the original title as inspiration. You can't estimate how long it takes to make a game from scratch in isolation from decisions about the scope, feature set and quality of the game, but maybe what you can do is compare it to budgets of other titles. This article http://www.nintendolife.com/news/2010/11/3ds_development_could_cost_triple_that_of_ds_software suggests NDS projects usually come in at approximately $53,000 to $527,000

Either those are incredibly skewed or they are talking about really crappy games.

I've worked on 7 DS games.  Each was a successful game, about as close to AAA as you can get on DS without actually being from Nintendo.  Each had a development budget of between 1.2M and 2.5M.  That is in addition non-development costs, such as first-party certification, marketing, and other costs which are generally as much or more than the development budget.

That was our budget WITH AN EXISTING ENGINE.  If we didn't have an engine I would estimate an additional quarter million or more.

So really, what you'll be doing is creating a new game from scratch using the original title as inspiration. You can't estimate how long it takes to make a game from scratch in isolation from decisions about the scope, feature set and quality of the game, but maybe what you can do is compare it to budgets of other titles. This article http://www.nintendolife.com/news/2010/11/3ds_development_could_cost_triple_that_of_ds_software suggests NDS projects usually come in at approximately $53,000 to $527,000, and using the industry standard $10,000 man month (http://www.altdevblogaday.com/2011/11/13/10000-is-the-magic-number/) for our back-of-the-envelope calculations, that buys you between 5 and 52 man months of dev time.

Either those sites are incredibly skewed or they are talking about really crappy games.

I've worked on 7 DS games.  Each was a successful game, about as close to AAA as you can get on DS without actually being from Nintendo.  Each had a development budget of between 1.2M and 2.5M.  That is in addition non-development costs, such as first-party certification, marketing, and other costs which are generally as much or more than the development budget.

That was our budget WITH AN EXISTING ENGINE.  If we didn't have an engine I would estimate an additional quarter million or more.