Oracle already has a number of guides to building a cheap Oracle RAC setup. One of the more interesting ones used a firewire device that could support multiple logins. Thus creating a cheap and fast shared storage device to use for ASM and OCFS. The article is here: http://www.oracle.com/technology/pub/articles/hunter_rac10gr2.html. The setup here was only a 2 node system. I'm not sure if these cheap firewire drives can handle 3 logins. There is another guide for doing iSCSI, although I would think the firewire setup would be cheaper and faster.