My DN is now 14. He doesn't normally acknowledge the gifts or say thanks, sometimes but not always. My Dsis sends me his wish list every year and every year i go

This year there was not one thing under $125. She called a few days later and asked what i was getting from the list because she didn't want to duplicate. I said sorry but nothing, it is all way out of my budget was there anything less expensive he was looking for? She said a video game but it is a brand new one and $60.
Now Dsis usually will make a very nice outfit for DD and her doll(s) for her bday. But for whatever reason she very rarely sends DS a bday present. His bday is in Nov. One year we were at her house for Tday and there was a gift, he was all excited thinking it was for him (he was 6). She said oh no that is for dad. He cried later to me and asked what he did wrong because we always get cousin a present. In fact we had DN's bday gift with us. Dsis just acted as if nothing was amiss. Dsis, DS and my Dad all have Nov bdays. So everyone was opening except for the little 6 year old. I felt so bad for him. He tried to put on a happy face but he just didn't get it.
For Christmas she usually sends him used toys DN has outgrown. Not a problem yet as DS is just happy to get something and thinks it cool it was from the big cousin.
However, I'm kind of tired of being asked to spend big bucks and then my son gets dissed. So this year I got a $30 gamestop gift card. I called my sis and asked if she got it, she sounded pretty annoyed and said yea and she was going to put it in an envelop for me. Not sure why because it was a decorative card in its own gamestop sleeve. whatever! no thank you just irritated response. I guess it wasn't enough.
I will still continue to give him gifts. He has a small family and I do love him. Someday I hope he will realize I did what I could and will see I was always thinking of him.
OP, I would reduce the amounts you are spending to where you are comfortable with what you are doing without a response. You should not feel obligated to give anyone a gift.