5000Rs for Valve Job.
Mechanic will charge around 1500 to 2000Rs
Plus the parts, like the Valve seals and all keep around 1500Rs for this.
Usually what happens is if you only fix your valves and your rings are weak the car will start giving blow.
If you want to get rings replaced as well add another 4000Rs to the above cost.
All above is just an estimate.