Hi, ruthy022002!
If you would like to post a draft copy of your letter here, without including any contact information, I'm sure that there will be those of us who'll be willing to advise you as to how you might make improvements to it. You know much more about what information that you need to include than any of us.
There are also links to questions that have been similar to yours on the bottom of this page that are similar to yours. You might want to click on them to see what some of the answers have been.
If you click on the following search, you might find one that's near to what you would want. You could then tailor it to fit your needs.
Sample Business Proposal Letter - Google Search
I wish for you only the best!
Thanks!