Hi, my name is Justin, and I am a software developer.
I can do the calculator app within the proposed budget and timeframe. I can do it in PhoneGap so that your app can be used on multiple mobile platforms, e.g. iPhone, Android, etc.
Otherwise at your preference, I can do it solely on one platform of your choice, either iPhone or Android.
After the app is completed, I can submit the app onto app store with your account, or mine, whichever you prefer. It's also possible if you prefer not to submit it onto the app store for public access; it's your choice.
Cheers,
Justin