Topic: From idea to launch in........

Just how fast is ROR?

I've been looking around and have been drawn by the claims that ROR can build a web app in "a fraction of the time" but am really struggling to put this in context.

Anyone have any examples of what they've launched and timescales (assume that the idea is well defined and we are talking from idea to launch)?  For simplicity, also assume that the database and wireframe mock ups have been properly designed and speciifed.

The reason I ask is that I want to build a website and am trying to figure out how long a project should take.  I know the "how long is a piece of string?" question comes to mind, but at least with examples I can at least make an educated guess.

I'm looking to build a site that's very very similar to www.universitytutor.com.  Essentially providers can add a profile to the site.  Users search on skill and location.  Results displayed on a google map sortable by charge rate and rating.  Users invited to rate providers and providers are charged a monthly fee for the privilege.

I posted the job on elance (http://www.elance.com/php/bid/main/proposalList.php?jobid=18878551 - if anyone is interested) and got one developer saying that it will take 400-450 hours of coding to get done.  Seems like a lot to me.

Any help would be greatly appreciated!

Anh