At 6000:-, you don't need to buy a blade for longer. I remember we had blades we called Rolls-Royce blades that cost around 2000.
When you rent a concrete saw, buy your own 300mm blade for 800 - 1500:- (300mm) if you search a bit. With that blade, you'll reach 9-10 cm deep (you can chip away the last cm with a sledgehammer). Sometimes it can be difficult to find a blade with the correct center hole (in those price ranges), but you can have the blade re-drilled for the center hole...
