One further piece of advice: the specs and the quote are a contract, which should be vetted by a lawyer who specializes in contract law. I would be very surprised if your customer does not have a lawyer on retainer, and I would be even more surprised if their lawyer does not try to ensure that the contract between you and your customer doesn't have clauses which would make successful fulfillment on your part virtually impossible.

Lawyers are also very good at finding ambiguities; your lawyer may have absolutely no clue what "HTML" or a "web page" is, she may also be able to find that item 37 ("Bug correction 12 months after delivery") contradicts state law and is void (so you've got to allow for an indefinite warranty) or item 104 ("screen colors and fonts") violates ADA.

I'm not a big fan of lawyers, but my experience is that corporate purchasing agents will not go out of their way to ensure vendors are promptly paid.