Digging graves, one of my favorite subjects. I am a grave digger for a local cemetary and we charge $300 per grave (we are thinking about raising the price). It can be a lot more work than you think. Even using a backhoe (which we can't do certain sections, not enough room) you hace to finish by hand to get the hole even, square and level. You have to have a means of hauling the excess dirt off (vault displaces quite a bit of dirt), and it can be a challange to guesstimate how much dirt to haul off. When back filling you have to pack the dirt around the vault by hand (about 4" of space around sides) or the dirt will settle unevenly and you will be going back to level it up a few times. Plan on investing in some 3/4" treated plywood to rest your hoe on to prevent tearing up the ground as you dig. The best way to get the grass to regrow is to remove the sod by hand, cutting it into square pieces (about 2' x 2' ) so you can lay it back on top after you fill. If you mound it right the sod will settle in even with the rest of the ground. Plan on recieving calls on Sunday morning as you are getting ready to leave to go fishing, picnicing, Sunday drive, etc. informing you they need a grave dug so they can bury someone Monday morning. Plan on staying and filling after dark in the winter because they scheduled the services late, took a wrong turn getting to the cemetary and showed up late. Plan on being a pallbearer at the cemetary because the family is small and they don't have enough people. The list goes on and on.
Hope all this helps
Ed King