That sounds a bit too steep for a price for the complete pair. I remember I once (2012) did the whole pair (Honda alloys, disc brake, drum brake, sprocket) for 13,000rs for a good friend of mine.
Rx115 would be a suitable option for the OP. Do not pay more then 8 to 9,000rs for just the disc brake however. Also make sure you get a master cylinder (Brake lever pump) that looks similar in size to the original Rx115's. Reason I say this is because karachi markets are full with small sized incompatible with rx115 master cylinders that have tiny useless pistons in them.