It is no surprise to me that your hardware vendor wants to continue to sell you expensive hardware. And it is no surprise that Oracle wants to sell you additional software (i.e., RAC). Both sides do have their points and obviously have a bias.
I am currently working on a project where I am replacing a high-end Sun server with smaller Sun servers clustered in a RAC environment. In our case, our costs will stay the same. We will just shift the costs from hardware to software. But in the end, we'll also get better scalability and better availability, which is also important to us.
I do know of many shops that have significantly reduced their costs as well. So the answer to your question all depends. So where do you go to get the answers? About the only place I know to determine which solution is best for you is to hire a consultant that specializes in this activity. While consultants are not cheap, this is not a long-term project either. It should not take too terribly long for your consultant to architect a solution for your company. Feel free to contact me offline for additional information.