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.
Ziad K. Abdelnour, President & CEO Blackhawk Partners, Inc, the New York_based advisory firm on such matters, puts it this way: "Giving a Letter of Intent only means 'Yes I'm intent to buy the goods but I can change my mind anytime.' A letter of Intent is not a binding contract. [Hence] The Letter of Intent is a total waste of time on a worthless piece of paper."