If what you want is a quotation or offer, then sending a letter of intent makes you look ignorant while requesting a quotation will generally at least make you look like you know what it is that you want. And what you want, after all, is a price quote. Hence you want to request a price quote, via a request for quotation.
To conclude, there's perhaps no more apt way to conclude this piece, than to quote this very fitting statement by contract law attorney, Ivan Hoffman, of California: "[Given that] the letter of intent is essentially a legally worthless document [but yet one that could potentially cause many serious legal problems for the signer]. It is not clear to me the reason any party would ever bother to create such a document and yet I have seen it used on many occasions."