Yes each dose lasts a month but a bottle lasts forever in number of doses.... I think I have a 500ml bottle for around that price, but I'm not adept at the conversion to 44oz ..... we've used it for so long I was almost wishing I had bought the smaller bottle! There isn't a date on the bottle so I have no idea how long it is good for. We don't have a bad problem around here so it's hard for me to compare products when they hardly get tested, but it works for us.
Just be careful letting the dogs back in the house until they are dry!
ETA - even if each spray is 1ml, I have 500 sprays and that would last us easily 12 months' worth of dosing.... and I dont spray in the winter. So it really is a lot of doses! You can go up to 2 sprays per lb but that's more for furry dogs, I think.