Sounds fair to me, I have a complex of 37 flats I do for £400 a month thats up to 40 foot though with some communal windows thrown in. So thats about a tenner a flat. Used to charge a bit more but was undercut

Being in one place makes a big difference, not having to reel in between properties speeds you up a lot obviously, but also dealing with one person, not collecting, not chatting, not having a tea or taking special requests makes a diff too.