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.
Proceeding with a clear understanding and agreement in principle: The key elements of the LOI should be negotiated beforehand and can be used as a guideline to prepare the purchase agreement. It should state that, if all information during due diligence confirms what was represented, that the buyer intends to complete the purchase under certain conditions. The key elements should include: