Can you tell us more about the furnace that's being offered? it would be hard for anyone to make any suggestion or comment about the price without seeing what is it that they are selling. A manufacturer, model number, job description and any special circumstances noted in the quote are needed for an answer that would make any sense price-wise.
You can always add more information to your question using the "Add New Comment" form on this page, and it also lets you post pictures if you have any - always helps with better answers.