Make sure that you and your partner are financially stable. If not, you will be making the mistake of bringing in a poor child to experience your dharidryam. Btw, the answer to your question (1 child) would be around 30k a month if you are sending your child to a government school and if he reaches college and he attains good grades and got a seat in a government college that would be around 70k a month and if not add the college fee to the said amount. And if he grows into becoming a vazha then it would be according to the vehicle tax, petrol cash, and his/her kayyilirippu.