That is not unreasonable. There are a handful of lawyers who do this work really well. Make sure you have someone good.
I am a former federal and State prosecutor and now handle criminal defense and personal injury/civil rights cases. Feel free to check out my web site and contact me at (212) 577-9797 or via email at Eric@RothsteinLawNY.com. I was named to the Super Lawyers list as one of the top attorneys in New York for 2012. No more than 5 percent of the lawyers in the state are selected by Super Lawyers. The above answer is for informational purposes only and not meant as legal advice.
Get quotes from other attorneys recommended by the local bar association to give you some peace of mind about reasonable fees.
The answer given does not imply that an attorney-client relationship has been established and your best course of action is to have legal representation in this matter.
Find several attorneys and compare fees versus services they suggest. There is no set fee for this so you will need to shop around.
Given the amount of work required, particularly if your mother has substantial assets - and it sounds from your description that she does - a fee of $5,300 does not sound unreasonable. However, if you're unsure, you should contact some other reputable estate planning attorneys in your area to see what they would charge for that work. I would suggest that you look up some estate planning attorneys in NY on Avvo and either email or telephone some of them to find out what their fees would be.
My answer does not constitute legal advice and may not be relied upon by anyone for any purpose and does not constitute an attorney/client relationship or an offer to form such a relationship. This disclaimer is intended to be fully compliant with the requirements of Treasury Department Circular 230 and the terms thereof are fully incorporated by reference. If you wish to consult with me please contact me at dana@nytaxcounsel or visit my website at www.nytaxcounsel.com