Pretty much what you have just described, one needs to pay for the yearly premium of the iOS developer programme in order to run custom code on your own device. Bear in mind that iOS apps are compiled in Xcode so one also needs to own hardware that runs OSX.

There are also people offering to sign you app with an enterprise certificate for a fee in the more dodgy corners of the internet but Apple is known to crack down on those once in a while as this obviously goes outside their ToS.