I purchase and cut a lot of slabs and sticker them to allow for seasoning. I have extra large slabs up to 6 feet in diameter sanded at a local facility for a reasonable fee. With a 37" belt sander, I have the ability to sand large slabs up to 220 grit. For small to medium slabs, I charge $25 to $50. Because of the significantly greater effort and time required, my fee for large slabs with one dimension less than 37" is $75 to $100.