Does anyone know how much these rings would be worth?

I have recently inherited my great grandmother's engagement and wedding rings. The bands are made of real I want to think 15 or 20 karat gold, the diamonds however are man made. They're from around the 1930's or perhaps 40's I'm not too sure. I was wondering if anyone knew how much they might be worth or where I could go to have them appraised, also how much would it cost to replace the diamonds with real ones? Thanks for answering. :)