Prostitution in Marriage?

Last class in our discussion about Mrs. Warren's profession, we talked about how Mary Wollestonecraft believed that marriage was a type of prostitution. I do not think that referring to marriage will automatically mean prostitution, but there are some cases in which this relationship does exist.
Prostitutes sell themselves in order to get money. Some women get married in order to get financial stability without necessarily being in love with the person they are getting married. What drives the actions of these two types of women? Money. So, what is the difference between these two? In the second case, women just sell themselves to one person for the rest of their lives, however in the first case women sell themselves to different men. It doesn't matter which situation we are talking about, for me, both of them are completely wrong. Both of these type of women lack respect for themselves and are damaging the sacred view of the union between men and women.
There is a specific example that I want to refer to in Crime and Punishment. Sonya prostitutes herself in order to get money for her siblings. She is selling herself to different men that will offer her money. In the other hand, Dunya is getting married with Luzhin. Luzhin takes advantage of Dunya’s situation when he proposes to her because he knows that she will be beholden to him financially. Thus, she will sacrifice herself for her family by getting married to him. Love is not part of these unions. Therefore, the only motif that drives the actions of these two women is money. So, what is the difference?
I think this a reality that still exists, although in a smaller amount than in the 19th Century. Nowadays, some people get married not in the basis of love but in the basis of economic stability.