This is a well-developed response that demonstrates clear understanding of Austen's complex presentation of marriage. Your recognition of her irony and use of contrasting characters is effective. The analysis shows good awareness of the text's subtleties.
Effective use of Charlotte and Elizabeth as contrasting examples
Good understanding of marriage as 'transaction' in Regency society
Step 1:
Analyse specific language choices more closely - look at the vocabulary of the opening paragraphs
Step 2:
Consider the narrative voice - how does Austen's narration create irony?