SA = Seeking Arrangement (dotcom).
Not to be confused with the common abbreviation for South Africa.
Basically a site where women can trade money for sex with men without thinking of themselves as a service provider.
Either on a one off basis, or for a monthly deposit in their bank accounts (hence "arrangement").
Think sugar daddy without any long term commitment.
Less transactional than AW, as there's usually no hourly rate, and often a social aspect involved too.
Think : "You can date me and bed me, but it'll cost you money".
That's my interpretation of what the site offers.