Attorney is charging more than we agreed upon

Hello, I am closing on a co-op on Monday and my lawyer sent me an invoice today which is significantly higher than what we agreed upon when we first talked. He told me he would do everything for $1000 because it was a small apartment and small asking price. I gave him a check for $500 when I signed the contract but now he is telling me I owe him $1250 upon closing for his attorney "closing fees". Do attorneys charge separate closing fees that were not disclosed beforehand? Is it normal for my attorney to be charging an extra $750 than we originally discussed? There was nothing out of the ordinary with the sale, everything went smoothly so I don't know when I'm being charged almost twice as much as we originally discussed.