In general, the cost of mining, milling and grinding 1 ton of rock in large-scale mining, has been calculated to be about $7/ton. Applied to olivine, it proposed that it would be about $12/ton.
The good news is that for the initial olivine, we will attempt to utilize "tailing" piles, which are the removed rock from existing mines. It turns out that diamonds, nickel, chromite, and other commodities are found in olivine-rich rocks. And to get to them, they have to dig up massive amounts of olivine that just sits on the site in piles as "waste."
Those tailings piles are also where some of the real-world calculations for olivine dissolution rates come from. They even determined that some mines hosted in olivine-rich rocks actually more than offset their own CO2 emissions in this unintentional way.
The ideal set up for a beach project would be right on the coast (in a tropical area as temperature affects the speed of weathering), near the end of a railway that runs from an abandoned mine with tons of tailings piles.