I'm one of the developers for Twitterrific and to be honest, I can't tell you how many hours have gone into the product. I can tell you everyone who upvoted the estimate of 160 hours for development and 40 hours for design is fricken' high. (I'd use another phrase, but this is my first post on Stack Overflow, so I'm being good.)

Twitterrific has had 4 major releases beginning with the iOS 1.0 (Jailbreak.) That's a lot of code, much of which is in the bit bucket (we refactor a lot with each major release.)

One thing that would be interesting to look at is the amount of time that we had to work on the iPad version. Apple set a product release date that gave us 60 days to do the development. (That was later extended by a week.)

We started the iPad development from scratch, but a lot of our underlying code (mostly models) was re-used. The development was done by two experienced iOS developers. One of them has even written a book: http://appdevmanual.com :-)

With such a short schedule, we worked some pretty long hours. Let's be conservative and say it's 10 hours per day for 6 days a week. That 60 hours for 9 weeks gives us 540 hours. With two developers, that's pretty close to 1,100 hours. Our rate for clients is $150 per hour giving $165,000 just for new code. Remember also that we were reusing a bunch existing code: I'm going to lowball the value of that code at $35,000 giving a total development cost of $200,000.

Anyone who's done serious iPhone development can tell you there's a lot of design work involved with any project. We had two designers working on that aspect of the product. They worked their asses off dealing with completely new interaction mechanics. Don't forget they didn't have any hardware to touch, either (LOTS of printouts!) Combined they spent at least 25 hours per week on the project. So 225 hours at $150/hr is about $34,000.

There are also other costs that many developer neglect to take into account: project management, testing, equipment. Again, if we lowball that figure at $16,000 we're at $250,000. This number falls in line with Jonathan Wight's (@schwa) $50-150K estimate with the 22 day Obama app.

Take another hit, dude.

Now if you want to build backend services for your app, that number's going to go up even more. Everyone seems surprised that Instagram chewed through $500K in venture funding to build a new frontend and backend. I'm not.