This is really a question about maintenance...
Ex and I have 1 dc together-9 years old.
Dc was unplanned and we split before dc was born.
Ex has always told me how much maintenance is was entitled too- I don't know his wage etc/ he is a bit of a story teller so don't know if I would believe him even if he told me an amount.
I have always felt bad at taking money as I had he final say over keeping the child.
Anyways when I mentioned i was struggling to a friend and that I asked for an increase last year for the first time and had to justify it to him to get it. When I said the new amount to a friend she was shocked it was so low.
More info
Dp and I have a dc also and we manage-its tight but we get there.
Ex also has a dd with his off-on girlfriend (who is lovely to our dc )
Ex himself is a bit of a let down to our dc. Irregular contact, no birthday, no Xmas.
I am starting to think the least he could do is pay proper maintenance-as grabby and mean as that my sound 
Anyways is £30 a week an okay amount?
It's more than some get.
How would you find out if he is paying a fair amount?
(All I want it to be is fair)