Price is the wrong first question. Two vendors at the same monthly number can deliver wildly different amounts of work, because most of the cost is labor and some shops put six hours a month into an account while others put twenty. So ask what ships. How many pages, how much content, how much profile work, how much technical, who writes it, and whether updates to your site are included or billed separately.
Be suspicious at both ends. Very cheap usually means an offshore template, automated directory submissions, spun content and a report generator, which can actively hurt you. Very expensive is sometimes real senior strategy and sometimes just an agency with an office downtown and account managers between you and the person doing the work. The useful question for an expensive quote is who specifically touches my account and how many hours.
Then judge it against lead value. If your average job is worth a few thousand dollars and SEO brings two extra jobs a month, almost any sane monthly fee pays for itself. If your average ticket is under a hundred dollars, the math is much tighter and you should be careful. Know your average job value and close rate before you shop. It turns a vague price conversation into a straightforward one about how many leads this needs to produce.
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