Question about a signed original oil painting?

Hi I was at a recent yard sale the other day, and came across a signed original oil painting. It was a very large painting. I didn't purchase it because of the frame but the painting was beautiful, it was an original by an artist that signed it Shaw on the left bottom corner. It was a Mediterranean scene with a boat docked at sunset. I'm going back today, and hopefully the lady still has it. How valuable would this painting be? She only wanted 25.00. I want to kick myself for not getting it, I could always get rid of the ugly frame on it....