When DIY makes sense
Doing it yourself removes the labor cost, which is the biggest single line on an installed job. For a small, flat, simple area with decent existing drainage, DIY can be a genuine saving — the work is mostly excavation, a compacted base, laying the turf, seaming, and brushing in infill.
DIY suits patient people with the right tools and a modest, forgiving site. The materials-only figure on the calculator shows roughly what the turf, base, and infill alone would run, so you can weigh the saving against the effort and the risk of getting it wrong.