You can spend as much as you like on raising a child.
"They can't lock people up who effectively hide their cash, or who look like they might pay at some point, because in jail they won't be earning. The other issue is that locking people up is expensive. It is only a deterrent if people know it can happen. "
They lock up people for tax evasion, even though it is expensive. However the punishment of having a criminal record and a suspended jail sentence would be enough for some men. Prehaps you could have a fines/ community service for a first offense.
Lots of jobs like accounancy will not employ someone with a finanical criminal record. Having a criminal record rules out someone becoming a teacher.
Somehow the message needs to be driven home that it is not acceptable to refuse to support your children.
"Op do you know what abject poverty is? are SS involved with this child?"
Povety is all relative. No social services do not routinely involve themselves with families living below the breadline. I know lots of families who are working poor and in povety by British standards.
It may well be true that no one is poor by ethopian standards, but relative povety is a serious issue. It is grim when a family can not afford simple pleasures like going to the sports centre for a swim for they stress when the school asks for money for an outing. Or they feel extreme embrassment when their child is given a small christmas present that they cannot recipocate.
If you don't believe there is povety in the UK then see
www.barnardos.org.uk/what_we_do/our_projects/child_poverty/child_poverty_what_is_poverty.htm