I practice law and agree that even agreeing to $1250 was unnecessary. Remember, as a client, you are in charge. Yes, the initial amount is an estimate, but as you pointed out, one of the errors was at their end, which means it should not cost you anything to have it fixed. Moreover, the fact that the initial estimate was a range, implies that the $1000 is the upper limit. For future reference, here's some language for flagging these things (both first shot at contacting and for standing your ground):
Assume: Mid-western law firm, where understatement and politeness wins over an outright attack.
Dear Lawyer,
Thank you for your invoice dated ____________. Per our notes, we see that the initial estimate was between $700-$1000. The invoice indicates an amount that is 2.5 times the ceiling of the estimate, and understandably, we are concerned. We request a revised invoice commensurate with the original estimate, considering that the final work product was not out of scope with the one initially requested by us.
Sincerely,
__________
By doing the above, you are flagging that this is a problem, and giving them opportunity to consider the issue and win you over by their excellent client service.
And if the lawyer responds to you with the weak sauce e-mail, follow-up like this:
Dear lawyer,
Thank you for your explanation, I recognize that discrepancies in accounting can and do occur. However, this was not a fixed fee arrangement, and the initial estimate quoted to us was a range based on the hourly billing arrangement. Our understanding is that $700 is the typical lower end of the fees, and if any changes or revisions to the work were to be requested, those would still be captured in the upper end of $1000. While we believe that the extent of the changes we requested did not warrant ____ hours of additional work at $ ____/hour billing rate, we are happy to pay the upper limit of $1000 for the work performed.
(Optional: If you have been generally happy with the work quality/lawyer expertise except for the pricing discrepancy) Except for this one issue, I have been generally happy with the work you have done for us and would consider referring you, should that need arise with my colleagues.
Sincerely,
Lawyers *love* referrals and any potential for one would mean that they are immediately on your side. So I would throw that in there if I was happy with the lawyer you were communicating with (assuming senior associate/managing partner). Believe it or not, sometimes excellent lawyers get stuck with sub-par accounting department and/or legal assistants and can't do anything about it if it's a large and bureaucratic law firm.