Although there are some minor condition issues (not surprising since more than 150 years old and in circulation, manufactured in 1862), this is a very desirable item. It is listed in the Scott US Specialized catalog as EP157. In the catalog, grading is mentioned as to encompass three areas:
1. Case will show signs of wear or handling and signs of original toning.
2. Mica will be intact with no pieces missing.
3. Stamp will be fresh with no signs of toning or wrinkling.
Catalog values in Scott are for very fine examples with mica intact, although signs of circulation are to be expected.
My Scott 2014 catalog shows the value to be $1000. I don't know if the 2015 valuation has changed, but expect it not to have much if any. As others, I agree the $40 is way too low of an offer. I would expect at least $150-200+,to be a reasonable dealer offer, and a pricing to collectors greater, perhaps $300-500, but it would take more time to find a buyer at that price. You may consider putting it in a coin or stamp auction to get a stronger realization than selling to a dealer or waiting to find a private buyer, but it will take longer to get your money (unless an advance is available). Also,
ebay is an option as a reserve auction or "Buy It Now".
Cheers and good luck. Dave