May i know the source of your information Dipankar?^You are wrong.Sandy bridge cpus will be extremely affordable.
Btw Sandy Bridge chip are cool and can be overclocked on air to high clock which means its crap basically with LN2. You won't get as high clock under LN2 as you would on air. And yes that's on cherry items not retail chips. Retail chip they struggle to reach 5Ghz on LN2.
To get the high clock rates on sandy Bridge you'll have to start with temps around 10 to get it up to 6. -193 you won't get that high
If it gets that high on air it will a big no no for LN2. It won't reach high clock rates on it