Does anyone know how I could send people notifications to people who would download my app I'm developing for iPhone?

Email them, duh once its in the app store it shos them when tgeres an update, just like eery other app

but how am I going to email them, its not like I have there adresses? and I’m not going to make them register, that would be massive pain

If they are testing your app then you should be able to contact them

Build in web functionality and have the app check your server when they press the “look for deals” button. I can guarantee people don’t want to constantly be spammed with your special offers, unless that’s specifically what the app is for.