While Ash was considering whether it was appropriate to ask for something so soon after just finishing her advancement to the current ranking she had reached, Ross broke her from her thoughts as he responded. "Just tell me what it is, and I will let you know once I have figured out the cost."
He saw Ash struggling, so he thought that it was best to see what it was that she needed so much.
There was no harm in her asking for something in advance since it was not going to be given to her until he approved of it.
Since he would not yet be giving it to her until it was assessed for the worth of such a request, Ash asking such a thing of him meant very little.
All that it would result in would be some time being taken to calculate the effort it would take to acquire such a thing that had been requested by her and to come up with a price or terms in exchange for it.