If it is truly just grass and irrigation, I’d guess
$1,000 – $2,000 if you do it yourself,
$1,500 – $3,000 if you hire out each task individually, get bids on each step and manage the schedule yourself.
$2,000 – $4,000 if you get a contractor to do it all.

But, if there are other things, like hardscape, planters, benches, decorations, borders, etc, you can probably double those.