Anyone interested in stones should have a good chat with Roger LaPointe of atomic athletic, they have both natural and honed granite spheres, prices and weights of the lighter stones as follows, prices rounded up to nearest whole dollar, price does not include freight:
25 pounds – $140USD
56 pounds – $200USD
75 pounds – $220USD
100 pounds – $260USD
140 pounds – $300USD
180 pounds – $360USD
220 pounds – $400USD
enjoy, ash