Hello mmmmm,
One way to estimate the value of an artwork is to look at the prices of similar works by the same artist at auction or private sale.
I see that you have tried this at ebay, but it would be a good idea to look at art auction directories such as Artprice (http://web.artprice.com/ ) or Askart (http://www.askart.com/ ) . However both of these require a small fee to access their database and have few listed works by George Crionas.
If you want an accurate valuation, Freeman Art (http://www.freemanart.ca/ ) will perform an accurate valuation from digital photographs for a fee of $US 45. requirements for the photographs and description can be found on this page (http://www.freemanart.ca/FreemanartFAQ.htm. )