I will give him credit to say that I do think Mr Collins goes by the book, so to speak. If he wants something, he will try to find a way to get it that is the most ‘proper’ or ‘upstanding’, once any of his personal desires are out of the way. I think if he decided he wanted to get married, and was looking for the best way to do that, it’s not impossible that he would think he should inquire in the Longbourn neighborhood first.

However, he is mostly the kind of person that finds a way to fit those best principles around his own desires (eg. pursuing Elizabeth because, of the Bennet daughters available, she is the most attractive but using the justification of her being the eldest). So I think he would have justified not marrying them somehow if there was someone else he wanted to pursue. The fact that he licked his wounds around Meryton after his rejection, rather than being excited there was someone back home he could now justify courting, also confirms to me that he didn’t really have other/better marriage options.

By this line of thinking, I am inclined to conclude that his choice to marry a Bennet daughter came about from other factors, and is certainly not as virtuous as he presents it. Which leads me to the following potential scenarios:

The first is that he wanted to get married, but he is just not a desirable person for anyone around him. In Hunsford and perhaps during his education, he was never able to capture the attention or praise or attraction of any of the women around him enough to get close to real courtship (or at least not with the women he would have wanted). The Miss Bennets, by familial connection to himself and by desiring to keep hold of the family estate, are likely more inclined in his favor. Not to mention the bonus points of being oh so generous to offer them ‘first dibs’ at keeping their estate, as it were. So if he wanted to be married, they are likely his best option for both establishing courtship and doing so without being turned down. His offer is the best option for his ego.

The second is that he didn’t really care to get married (yet) but that Lady Catherine, after learning of the Longbourn entail, was ranting about how it wasn’t right and that she would never let her estate be entailed away and how terrible a thing it is for the Miss Bennets. And that this rant was followed by her telling Mr Collins that the most proper thing to do would be to marry one of them. Mr Collins, never one to oppose her, immediately agreed to it and went on his way. He never really had anyone else in mind and figured it would be a flattering look to be so generous and condescending as to marry one of the Bennet daughters. His offer is best to score bonus points as a good clergyman.

The third, and my personal favorite, is that he accidentally wound up getting shipped off to marry a Bennet after he severely overestimated his hand with Anne de Bourgh. Considering he misinterprets Lady Catherine’s micromanaging tendencies and taste for flattery as interest in himself personally, I think it’s possible that he also misread his invitations to socialize at Rosings as more than they were. Believing himself a favorite at Rosings, and interested in Anne for her fortune/social status, he may have decided to start a conversation about marriage in order to test the waters or try to get a more established courtship started. And whether or not Lady Catherine understood his intentions for this dialogue, she hears that he is looking to get married and instead directs him to the Miss Bennets. And once she has decided on something, it will happen, so off he goes. The offer is kind of by accident.