Was their a cut off on the estimate? I put a 30 day guarantee on estimates. If you didnt include something like that, you might have to bite the bullet and do the work.
I bid a job on Friday that was a mulch job. I called around, found one local store that had what I needed, the rest were out if stock. We live in a small town, so finding materials can be challenge. When i went to pick up the materials saturday...they made a mistake and DIDNT have what I needed in stock. Instead I had to drive 150 miles round trip to go to "Large home Improvement Store" to get all the materials I needed. Because I had already given the estimate, I ate it, and did the job anyways. I managed to make a whopping 6 dollars an hour for the 2.5 hour job if you dont include the drive time. Outstanding huh...LOL.
But in the end, the customer was very happy with the work, and will refer me to others, so I guess thats a plus.
So to answer your question, if there was no time cutoff on the estimate, and its a good customer you want to keep, you may want to do the work, as long as it wont cost you TOO much. Even if its not a regular customer...how might an increase estimate affect future jobs, and your buisness reputation. just a few things to consider, because from what ive seen (especially in a smaller town), word travels fast, and word of mouth is by far the best advertising that I know of.