You should have talked to him already. You coming up with your story that you won't be going due to expense may have seemed to everyone like you just not wanting to go, which is obviously not the case. You hoping he would intuit your unspoken wish and give you the trip as a birthday gift is just fairytale thinking.

It's not too late, you could tell him you really wish you were going and ask if he could subsidize you. I honestly don't know why you haven't done it already.