Para nako dili naman usik-usik ug kwarta ang thermal paste na nindot. What is 500php for 3years worth of paste? Whats a waste is putting excessive amount on the surface. Very small amounts is needed really. It will take some time before you can exhaust 20mg. Good TIMs are good investments in my opinion.
Besides, if you watercool or change air-coolers often, youll have lots of spare TIMs lying around.