Head gasket its self is just of Rs 300 (good quality local) but if you go for original which is also very hard to find now will cost you around 2K.
The thing is disassembling half of the engine to reach it.
On the way back you might have to replace timing belt , T.B bearing, TB cover, engine oil, oil filter, coolant, clamps, various gaskets and pipes, broken bolts etc which will easily touch figure of 5K. and if the mechanic says your head needs a valve job then another 5K. This is excluding Labour charges.
They will say "sahib jee kuhla hua hay karwa lo"
So keep your pocket wide open.
Have you checked the PCV ??