All amounts in USD.
I'd say the calculus for "should we make an app" matters strongly WHY you're making an app.
Many companies make "prestige" apps. These have little functionality, and are mostly toys or are basically sophisticated marketing materials. An example of this type of app: http://www.adweek.com/aw/content_display/news/digital/e3i2e2... [Coca-Cola]
Should you make this type of app? If you already have name recognition, or your industry functions off of it, YES. This type of application can basically be something that people toss away, but just like much of advertising, may make your customers take notice and remember you.
If your industry does NOT function off name recognition, I don't really see why this type of application is useful for you to make. They often disappoint people who want hardcore integration with your products and services, so they aren't without cost (not even costing development cost).
Now should you create a client/tie-in app for your business? It depends. If you work off of some sort of information that the iPhone can collect (even "Where is the user"), then really look at a strong case for developing an app. Functions the application can access are: Where is the user, what's a picture of something the user is near, how fast is the user moving, what is the user's email, what is the user's contacts, what are the user's phone numbers, shall the user call you right now, and would the user like to hear something right now. Odd pieces to consider separately, but depending on your industry, they may be appropriate. If you're a paint company, pictures of their room which you then make an app to show their walls (or even have real people doing mockups for them) could be a good selling tool. If you're a home improvement company, pictures of the job could be a great thing (see the excellent "JuJu List app" for an example of this) for making a good quote. If you're a company that needs to show a local area to users (say, here are our locations, or here is our delivery zone), then the app can do well for you. But remember, if people think your app COULD do something, they may go away disappointed if it doesn't.
For instance, if your company repairs heating and A/C, if the app doesn't show them the status of their call, and estimated time of the driver, you'll very possibly get negative reviews, bad press, etc (then again, bad press can be better than no press).
Additionally, iPhone apps are not inherently expensive. You can get them done for under 10k, but you have to listen what's cheap, what's not, and be willing to cancel what's not. Lots of medium to large size companies involve way too many people and expensive measures, and end up spending 40-200k internally and 20-150k externally before they get their app out the door due to overmanagement. Ideally, this sort of thing should be a 1-3 person job lightly managed at a company.