Apple developer program is of 3 types
-> university program
-> IOS developer program for $99
-> IOS developer Enterprise program for $199
university program is free of cost any body can get it just by logging in to apple website , all development tools like Xcode(only Gold Master) is available for free of cost to all and apps can be tested only on Simulator but not on device
IOS developer program is good if you are intend to distribute the apps on app store ,with this account you can access the developer resources like beta version of Xcode and WWDC videos and test your application on actual device and number of device is limited to 100.
IOS developer Enterprise program is helpful when you are intended to develop an application for in house distribution with out uploading to app store i.e. apps for particular company or agency or sector.
it all worth based on your requirement if any one don't have prior IOS experience on IOS university program is very helpful to learn and do some R&D in order to learn cocoa development.Once you are familiar with it you can register to Developer program to start developing actual app.
you can start develop application without registering also but you can't test on original device (some time app will behave differently on device when considered to simulator for particular instances) so its safe to use original device.
if you want to upload app to App Store developer account is must. for more detail go through this website
iOS Developer Program
