Very expensive, unless you only need to use it during peak traffic hours. A month runs you over 700$, and I'm renting a dual quad core with 32GB of RAM, plus bandwidth for 450$ right now.
If your load has predictable peaks it may make a lot of sense to spin up 1 quadruple extra large server rather than the equivalent number of large instances, particularly if you're talking about something like a memcached server.
Where from if you don't mind me asking?
A small-ish company called 478east(www.478east.com). They offer relatively cheap high-end hardware in their LA point of presence, but lack a fancy control panel like SoftLayer.
Their $450/mo offering seems to have only 8GB RAM.
It's a custom order, they don't list everything they offer, you have to ask.