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As for costs, anything that needs XCode requires a yearly fee of $100 to Apple. You will likely also want to distribute over the App Store, ....
I am not sure thats actually the case. My application, tomboy-ng is pure Lazarus but I require XCode tools to build it. I do not pay Apple's $100 extortion, end users have to hold down a key when first starting the app, after that its OK. I do not distribute it via the App Store.
I appear to have a number of happy Mac users. Mainly I expect, ones who are, for what ever reason, forced to swap platforms regularly. One of the app's key features is its ability to sync its data between (cross) platforms.
Davo