I am applying to a proposal where they are asking for a flat project fee. I usually work based on flat project fees, so how / where can I list that type of pricing? Also, is there any way to note a range? Some things just depend.
Are you referring to applying to fixed price jobs? You should be able to bid with the amount you want to be paid for the project and submit it under Terms. Unfortunately, it's not possible to bid with a range!
Along with Bojan's advice, you certainly can state a range within your quote. In other words, add verbiage that covers eventualities that can occur with a project, like scope creep. Include text that makes sure your bases are covered, especially with new clients. Just be clear about what your bid includes, and that anything over and above that may incur extra charges/milestones ... because you're right, some things just depend.