Honda 78*C thermostat was about Rs 1500/- for a brand new item, used ones may or may not work like they should.
@usman505 - your engine uses the regular suzuki thermostat that is 82*C rated - there is a pipe in your engine that causes major problem, that pipe is the water pump inlet pipe that goes under the exhaust manifold, it corrodes internally and collapses to about only 20% diameter of original and causes heat up.
Check that with a mirror and torch after removing bottom radiator pipe from it. Replace it if you see corrossion.