Jane Austen should be considered a moralist and a social critic rather than a snob. A snob is one who treats people condescendingly. Austen uses both the characters Mrs. Bennet and Mr. Collins to point out common, morally questionable social issues rather than to poke fun and judge herself as superior to either character.
It is pointed out from the very beginning of the book that Mrs. Bennet is a very ridiculous person who frequently acts with impropriety. She allows her youngest daughters Kitty and Lydia to walk to Meryton daily to flirt with the officers and her own manners in society are extremely poor. One instance is seen at the Netherfield ball when Mrs. Bennet is overheard talking to Lady Lucas "freely, openly, and of nothing else but her expectation that Jane would be soon married to Mr. Bingley" (Vol. 1, Ch. 18). It is of course a gross social blunder to publicly speak of the prospect of a marriage, in the house of the man in question, well before an engagement has actually taken place. Mrs. Bennet acts equally poorly when Lydia runs off with Wickham and worse still once they have finally been forced to marry. However, Austen's point is not necessarily to treat such a person as Mrs. Bennet condescendingly, but rather to point out the fact that women like Mrs. Bennet truly do exist in society and, more importantly, to point out the consequences of such behavior, such as family disgrace.
Mr. Collins is also recognized as an equally ridiculous person. What makes him most ridiculous is his contradictory nature. He was raised humbly by an illiterate father and is now a clergyman, but he also thinks far too highly of himself and his vanity is fed by the attentions Lady Catherine de Bourgh has paid him (Vol. 1, Ch. 15). The ridiculousness of his contradictory nature is particularly seen in the letter he addresses to Mr. Bennet upon learning of Lydia's elopement. On the one hand, like a clergyman, he offers his condolences and his deepest sympathy, but on the other hand, like a vain, arrogant person, he says he has relayed the whole affair to Lady Catherine, feels that all of the daughters will now suffer due to Lydia's behavior, expresses gratitude at having not married into the Bennet family last November, and advises Mr. Bennet to cut off his daughter. Again, Austen's point, rather than to condescendingly make fun of such behavior, just as Mr. Collins does, is to show that such people, even clergyman, really do exist in society and to point out the wrongfulness and social dangers of such behavior.