Not sure how the extra supply for grapes affect retail prices of grapes for regular consumption. But at Costco in Southern CA, the price of grapes have been fairly stable (~$5.99 - $7.99) over the last year or a little more.

California’s wine grapes (vitis vinifera) aren’t suitable for eating. Some varieties (vitis labrusca) can be used for table grapes or wine grapes, but those aren’t really grown in California.