The first and the main purpose of your cover letter is to connect your project with the potential reader's funding mission. It usually appears from the very beginning of the grant proposal. However, don't think that it is the same as the summary determining the key points of your proposal. This is more creative and sometimes even more challenging task, in order to complete which you need to be very serious about it. The truth is, it is usually hard to find a proposal cover letter sample for the reason that real applicants don't like their cover letter to be published on the internet. In addition, cover letters differ depending on the specificities of your research project, the characteristics of the funding organization and the funders as well. At the same time, even if you have found a good sample, it doesn't mean that you should precisely follow it because you may have another purpose, objective, etc. Anyway, you should know basic requirement for writing cover letters.