posted 02-19-2008 09:48 PM
Jim, my personal opinion here...You are right on supply and demand. They are the most common signed Grissom item on the market. But the flip side of that coin is that they are authentic, and usually totally filled out in his hand.
Of course, they are not as desirable as say a signed photo, but still considering it has his signature, his handwriting, and is a snapshot of his life, they are a terrific item to own.
They do sell for that range you state above, but I personally value them at well more than that. I have owned a few of Gus's checks over the last few years and considered each one a unique and affordable addition to my collection!
Go get one, you will thank me 
Jay