It depends on how polished you are looking to get and how much experience you have with Photoshop/Illustrator and general front-end development.
If you are simply looking to get some iOS experience, you should be able to hack together the UX/UI yourself. If you are trying to launch a business, design will be imperative for success. Show me 1 poorly designed, truly successful App in the App Store.
Like everyone says now-a-days... I'd suggest focusing on the MVP concept and build just the core features, with excellent design and UX.