It's not an unreasonable amount, and the fees were not increased because you called to pay the mortgage current. Neither mortgage company nor the attorney are "helping homeowners." They are simply collecting on the mortgage.
It sounds like your assumption that the fees are too high is based on the number of days between the letter and your call. Legal fees are usually based on either an hourly rate for the work, or a flat fee for the work. Both can vary quite a bit, but it's not hard at all to do more than $1000 worth of legal work in a week. You should also realize that at least some of the work was done before the letter was sent - it's necessary to review the documents and prepare the letter, prepare and file a Notice of Foreclosure in the county real property records. There was probably a title check to confirm other liens, especially tax liens, (since these require separate, additional notices) and most likely at least some of the documents necessary after the foreclosure were drafted.
Hope this answers your question.