I was thinking the very same thing only today!
At the moment I offer a monthly, Bi-Monthly and One Off's
If monthly £10 20 30 40
Bi-monthly £15 27.50 40 54
One off £20 40 60 80
As you can see the One offs seem a bit steep (I have had some laughs on that)
Not many takers on one offs...
But having said that I am at home NOW because of a One Off this morning £110
In and Out (Trad
)
so it does work (sometimes!)