2 Pair left. Basically this gang... $20.00 per rotor for the machine work. I don't think you'll find that anywhere.
Other things to consider: Proper diameter for a 914-4 rear caliper. No need to machine a 914-6 rotor to fit and, again, the rotor attachment screw holes are both in place. If you have -4 rear calipers and/or -4 drilled hubs, these are the least expensive option. Why purchase expensive 914-6 rear rotors and pay extra to machine the edge on those, only to find out the attachment holes don't line up (914-6's used 911 hubs with a different layout)?