It looks like dev mode activation is free at the moment. No telling how long this will last, but you don't even need an Xbox to activate dev mode so people may as well sign up while they can. Dev mode will be needed for UWP homebrew, and would be a one-off $19 payment otherwise.
https://www.microsoft.com/en-us/p/dev-mode-activation/9vwgnh0vbn60
EDIT - Apparently you do still need to pay for a Partner account. Apologies.
EDIT 2 - You can get a free Partner account at https://developer.microsoft.com/en-us/windows/rewards
Thanks to Mazkarth for the information.
https://www.microsoft.com/en-us/p/dev-mode-activation/9vwgnh0vbn60
EDIT - Apparently you do still need to pay for a Partner account. Apologies.
EDIT 2 - You can get a free Partner account at https://developer.microsoft.com/en-us/windows/rewards
Thanks to Mazkarth for the information.
