I have a probate matter pending, and the attorney fees/costs/bill (not sure of correct word) have gone up beyond what I was expecting. Would it be considered gauche to ask for an accounting from my attorney? On the one hand, I just want to see this matter resolved. On the other hand, it's gone up by about $800, of which I'm on the hook for half.

Each bill should include a detailed statement of the work performed and if you have questions about it, you should ask. If you aren't getting detailed billing, you should feel free to ask for it (require it) unless it is a fixed fee engagement (but, if it was fixed fee, you wouldn't have posted this).

FPNI x 2, you need to be getting itemized bills on any legal matter and if you have questions, then question them about it and what was done to justify the bill.  I don't give anyone freedom reign when it comes to my money.

Bill should be itemized. It is hard to predict how much a matter will ultimately cost if being billed by the hour. I do a lot of litigation, and I tell people up front that I can only control one half the work and the other side dictates the other. I also quote on the high side. If I think I can handle a case for $50k, I’ll quote an estimate of 60-70k. That way they are either happy when it comes back less than quoted, or if it runs over what I expected, they aren’t surprised. Litigation is a bit of an outlier, as it is very, very unpredictable.

Keep in mind that probate billing is still, in some places, controlled by local schedules that are based on the value of the estate.  You written fee agreement with the attorney should have disclosed the type of billing involved in your matter.