This is not likely to affect your resale. Everyone *should* pull permits all the time, but honestly - it doesnt always happen.
Next time - pull a permit first.
The real issue is this - was the work performed to code? If the work was performed to code, then not having a permit is not as large an issue. The problem most people have is that when work is not permitted, the contractor can take shortcuts that they otherwise would not be to take.
The real cost will be if the building inspector requires you to correct things in order to issue the permit.