That fee sounds a tiny bit on the high side, but not startlingly so. My guess is the $20,000 is for full jury trial, etc.
Now, what you need to know is that some lawyers will encourage you to battle over every little thing, and it racks up their fee considerably. Some will simply go along with your own wish not to give in on anything, and they make the same kind of money as if it was their idea.
The BEST lawyers will give you a good picture of how you are likely to make out if you pull out all the stops, but counsel you to consider settling for something less than you feel you want or deserve. And, as LTD points out, to the extent you can agree on certain issues with your STBX, there is less to fight about. You can also hire a mediator to help work out an agreement between the two of you. A lot depends on your individual situation and your bottom line on what you are willing to accept.
I got divorced pretty cheaply the first time, because my ex and I were able to agree on EVERYTHING. We each had our own lawyer to make sure we weren't shooting ourselves in the foot, but we told the lawyers what we wanted, and it was just a matter of drafting the paperwork. In my second divorce, we had no kids, few assets and debts, and I handled the whole thing myself (I happen to be a lawyer, but it was so simple anyone could do it when there was nothing to fight about).
Take your time, think about all your options.