Phone only sales?

I am trying to find a deal on a phone only, without trade in, as the phone is too old to receive a trade in credit for. I am wanting to trade in a iphone 8 plus for a 15 plus and am being told via the trade in tool (and chat) that the 8 plus is ineligible for trade in. However, apple will accept it as a trade in.

I'm hoping that I am able to receive a trade in credit from xfinity or I'll likely purchase from Apple directly. I'd prefer to purchase from xfinity to keep my business with them but I also need to look at saving money. 

The other option would be to receive a discount on the 15+. I don't want to upgrade any lines or add any lines as I don't need that and it won't be cost effective for me. 

I feel that I should still be eligible for some sort of discount especially as I've been with xfinity mobile from the beginning.

Please reach out if someone is able to help me with one of these items. I'm looking to make a purchase fairly soon as a Christmas gift. 

I know there have been $200 offered as in xfinity awards but unfortunately, I was not looking to purchase at that time.

Thank you.