I said:
Do you know if it is legal to sell sperm in this way?.
'In this way' refers to flogging sperm on the net, in personal ads etc.
This means
first find out if it is legal to sell sperm outside of a legit sperm bank. That's just commonsense, but it's obviously in short supply round here.
Actually, the legal ramifications are just one of the reasons to be cautious. What if the woman decides she would like the father to contribuite funds afterall, tracks him down, threatens to kill herself, harm the child etc etc. Sounds like an unlikely scenario? Well, you'd better hope so if you want to donate sperm to someone you don't know. You just don't need that kind of hassle. There's too much potential for things to go badly wrong, regardless of whether you are donating legally or not.
There are other things to consider if you're doing an 'under the table' donation (interesting image!). I wouldn't feel confortable giving sperm to somebody I wasn't absolutely convinced was going to raise the child well. I would hate to think that my son or daughter was being mistreated by a weirdo parent who just wanted some kind of trophy child.
Some people may be able to 'fire and forget' but I don't think I could bring myself to do it, certainly not for pocket money. What about half a mill?....well, I may have to consider adjusting my moral parameters for that amount

, if anyone was dumb enough to offer me that much for my seed!