SNB-E definitely won't be cheap -- they are Intel's new extreme-performance chips. They will likely be $500, $700, and $1,000 for the three introductory models. You will also need an X79 mainboard and a quad-channel memory kit.
IVB will likely be a little more expensive than current SNB processors. They are the mainstream replacement for current SNB CPUs, and will be compatible with most current 1155 mainboards after a BIOS update.