I’d say hold out on the cage until you make it into the 11’s. 11.49 is the cutoff for a cage,I’d invest in a good helmet and harness before getting a cage because that stuff is more important at your current rate of speed.
Do you have a driveshaft loop? Plus if you go faster than 11.49 you’ll need a few other things.Flywheel shield,extinguisher,fireproof jacket,harness.