According to the CSA website, if your net income is more than �200 per week, you will be paying 20% of your net income to your wife (based on two children of yours living with her). This is reduced if you have other children to support. It's 15% for one child and 25% for three. Again, the figure is reduced if they stay with you regularly. The CSA doesn't appear to be as harsh as it once was, so you should be able to treat the boys to days out/holidays and help with school uniforms etc.
This calculation is (according to the website) for new applicants..........before anyone attacks me because they're paying more!!! lol.
I think you'll be surprised at how well off your wife could be if she got herself a part-time job of 16 hours per week and claimed working tax credits.
Another friend, with two kids of similar ages to yours, works full-time. However, child tax credit pays for ALL of the childcare and she ends up with:-
�1300 through work
�300 from ex hubby
�120 child benefit
�350 working tax credit
�400 child tax credit
Okay, so the �400 goes straight on childcare but the rest is hers. Mortgage is only �500 per month and she's laughing.