<i> And she refuses to let him have any contact with the child! </i>
it doesn't matter what she does or doesn't want to happen. go to the courts and get court ordered visitation. then if she interfers with the visitation she will be in contempt of the order.
if a support order is in place, then your state guidelines should have be the decising figure on the amount. it probably isn't what you want to hear, but he played and now he pays. it may work out that he needs to take a second job to pay the support. it may work out that things will not be as "nice" as they once where. you may not be able to go out and eat with the family a couple times a week. the luxuries may not come around as often as necessary. but that is something that your husband should have taken into consideration before he slept with her. (i would feel the same way if the woman was complaining about being pregnant.) that is something that possibly can happen when two people have sex - even if they use protection.
instead of being upset that she used him to get pregnant and to get the support money - you should be upset that your husband put you and your family into this situation. then you should get over all of it.
there is a tiny baby that has been brought into this world. for whatever reason. that baby deserves love and attention from both of his parents. he/she also deserves support from both parents. forgive your husband, and try to forgive the mother, but don't hold it against the baby.
another point on this - anyone who actually believes that a girl would get pregnant to get moeny - come on. let's see - the expense of having a child runs up to $5,000 and then there is the expense of raising a child for the next 18 years. what do you figure she will spend on raising that child over this period of time. 50,000 maybe 100,000. you are so right - she did it for the $50 a month. great investment.