My Enermax 350 recently died after just two years of use.
I replaced it with a Seasonic Super Tornado 400, which is
working fine with my SK8V mainboard and Opteron 142 CPU.
Better question is, what do you need to spend to support the
particular system safely and promote good lifespan. It's
not simply a matter of declaring what you're willing to
spend, sort-of the opposite, that you don't have much choice
but to spend *what's necessary* to achive the result.