Estimation using Rational Unified Proces

I have read several good books regarding the Rational Unified Process and am interested in learning more. Here is my question: typically, our business partners want to know in advance how much a project will cost and how long it will take. With numerous iterations, has someone developed reliable methods for estimation when using RUP as the SDLC?

We’ve never had great luck with lines of code or function point methods. Would be interested in estimation methods beyond LOC or function points.