As I said earlier, weight in grams is more helpful.
1300g and under is usually worth more than 1500g and over. Thin is in. That is why it affects the expected price.
An 18 inch is considered probably a crash/ride. A more recent eBay auction has one that sold for $949.00.
There are a few old stamps going in that range in the completed listings. Not new stamps, or intermediate stamps that I can see.
Again, check completed and sold auctions on eBay for your best idea for what to sell it for.
Alas, because new stamps usually fetch lower prices than old stamps, sending somebody off to completed listings without more info on just what factors matter may not be the best thing for them.
However, you can look here in this recent thread:
http://www.vintagedrumforum.com/showpost.php?p=291440&postcount=44
If you used $949 as an expected value for a new stamp that would be a good example of over estimation due to confirmation bias (I talk about that briefly in the post I linked to). Not that backbeatkeeper was suggesting you use that one value of $949. But just to drop in a more realistic value at this point, the completed listings show this new stamp 18" at 1390g which went for $525 on Dec 5, 2013.
[ame]http://www.ebay.com/itm/190993223578[/ame]
Now that I've seen them I may have to go and record the several old stamp 18s which sold at above $800 and consider updating my ranges. But then I have to record more sales to make sure I get the bottom of the range right as well...it takes a lot of work to do these things to best practice. *sigh*