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.
A famous example often cited by legal scholars, was a case involving the Getty Oil and Pennzoil in very early 1984. The parties had signed a "Memorandum of Agreement" _ viewed by the parties at the time as a Letter of Intent _ for a complex investment and stock transaction, whereby Pennzoil would purchase Getty Oil stock, and set forth general terms of the investment that had been reached in conversations, and also stipulated that the Memorandum was subject to the approval of the Board of Getty Oil. The Board of Getty Oil sooner approved the transaction and both parties announced on January 4, 1984 in a press release, an "agreement in principle" to the terms of the Memorandum. The final agreements for the merging of Texaco and Getty Oil were signed by the parties on January 6 _ 8.