Hi, any collector would be happy to get genuine stone marbles from the 16th through 19th century, although most are very dull shades of gray and brown. I don't know that I'd pay more than $20 for a small pile of them unless it had a lot of variety or interesting colors. Some prettier antique "marble marbles" and pinkish "blood alley" types with red lines are certainly worth a few $ each though I rarely see them for sale. My personal favorite are the dyed hand cut and polished German agate marbles from the late 19th century, especially the bullseye types with high contrast bands. Typical nice examples fetch $5 to $30 each but fancy examples in bigger sizes or rarer colors like green and blue can command $40 to $60 each or more on occasion. Note that these are vintage ones evidenced by the hand-faceting channels visible on the surface under strong light or a loupe. Some vintage marble collectors also fancy the contemporary mineral spheres which some would call marbles, simply for their beauty.