Johnny Depp spends "Over $150,000/month on full-time security for his children" according to current revelations. So $900K/year for someone who's not very famous isn't unreasonable I suppose.
It's easy to work out the cost of full time security. Lets say you need 2 people on rotation, they do 12 hours per day each (doable because they get to relax while client is at home etc.) then multiply by a reasonable salary for skilled labor like 70k then you get to 140k per year per person easily.