Dafodil, We pay about that figure.
What you need to consider is what you get for your money & if you feel happy that you are not being ripped off.
I know that other people pay a lot less than me for their maintenance but its all about you being comfortable with the service you get. If they are giving crap service and the garden is overun with weeds etc then you are not spending your money wisely. Likewise if its trouble free and all the gardens are looking great when you get there etc then fine. If you can get cheaper and equally good service then even better.
Its a bit like putting your car in for a service. The main dealer will probably charge double per hour than a local small garage but people still use main dealers because they think its best. You are buying a service with maintenance, how good or bad it is is a subjective view.