Au Pair Visa versus Working Student Visa?

Hi!
I've been having trouble finding some definitive
information and I'm hoping some of you can help, with experience or
pointing me in the direction of info.

I'm an American talking
with a family in France right now. They mentioned something about
getting a 'working student' visa instead of an 'au pair' visa because of
some subsidies they could get from the government. They are just
looking into it from their end and asked me to look into it from mine. A
pro and con list or something. I know that, as an American, I have to
take 8-10 hours of french lessons for an au pair visa, so I'm trying to
compare that to the student one.

So the questions are
- have
any of you gotten a student visa instead of an au pair visa?
- How
many hours of class do you have to sign up for with a student visa?
-
Does it cost any extra on my end?
- Can I get into a school even if
I've graduated college?
- Could I just get accepted to a French language school or does it have to be a university?
- Do I have to take more than just french
classes?

--I've heard that some universities are only 300€ a
year? This seems odd to me....True?

Any info you have would be
great. I've been looking everywhere and unfortunately there aren't any many active au pair forums I could ask.

Thanks!

~Nikki