Okay, for one thing, a cage is only heavy depending on the material it's constructed from, even steel cages can be pretty light if the tubing is hollow and not too big for your application
also, they serve other purposes too. they help stiffen up the chassis which is major if you autocross, and your car is a unibody hatchback like the celica.
You also mount your harnesses to them, btw.
Of course, they make pillar bars, harness bars and floor bars, which could be a good investment if you don't want to put a full cage in your car, but want the added stiffening benifits.
Don't forget strut braces too.
BTW, if you want the safety benifits of a cage, you had better weld it in rather than bolt it in. If you roll, and it's bolted in the car, the bolts can shear, and you now have a metal cage bouncing around inside the car with you. not a good idea.