Well if you are looking to spend minimum, then you can consider getting Ring Spanner (Ring Pana), only. That should cost you Rs.1000 maximum, for required ones. I mean, a single Ring Spanner has TWO Holes. You can get combos like, 8mm&9mm, 10mm&12mm, 20mm&22mm etc etc.
You will be able to open up: Head/Tappet Cover, Spark Plug, and Engine Oil Drain Nut ONLY.
To open up the the Magneto Cover and Air Filter cover, you are better off buying a Goti Set, with a Goti Extender. Once again, you don't have to buy the complete Set. For good quality, you can get "Raider Goti", which is German Quality but China Maal ... are priced reasonably and are quite durable. (They are of Silver Color, with a Blur Strip around them, and "Raider" name is tagged).
I hope its enough.