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.
"Letters of Intent, legally, are the worst of all worlds. Writing a letter of intent is not to be taken lightly. In law, you either have a contract or you don't. LOI's are the legal equivalent of "almost pregnant." Letters of Intent emphatically state that. They state that they are not formal agreements, and then often proceed to set forth agreed terms of the proposed transaction. Given this paradox, if the deal goes sour, one party can argue [in court] that those agreed_upon points were, in fact, agreed upon _ or, in fact, a binding contract. And, in some cases, furthermore, that the party relied on the LOI and has monetary damages based on such reliance."