Hi Danie,
Without an Apple dev. account, you won't be able to provision your device to run the app, nor any Apple device for your in house App (for your client)
It seems with xCode 7, you no longer need an app dev account, but I didn't tried that.
So you can try with xCode 7.
Or you can Jailbreak your device, in that case you try with JailCoder:
http://oneiros.altervista.org/jailcoder/
But the best is getting an apple dev account, you will be able to add 100 ad-hoc provisioning devices, it's worth it, and you will be able to deploy it for your client, I agree paying US$99 for just testing on your own device is a nonsense, but for deploying for few devices, and getting the Apple store, it makes sense.
Patrick