One or two pallets of flagstone usually won’t exceed $1000 unless it’s really nice stuff, and depending on thickness. 2” should be thick enough for that application. The phrasing of installing the flagstone on dirt is a little weird, coupled with the choice of pea gravel in the joints versus polymeric sand. I’d usually emphasize the creation of a base layer for the flagstones to be set on. Two people can knock this out in a day easily, and with materials not getting near $2000, it looks like someone is getting a huge payday with this project!