Anyone know a good place to buy them for cheap?
If you can find an NTK dealer, the PN is OZA527-E4 per: http://www.ntklambdasensors.co.uk/main/ferrarintk.htm Also click on the "info" button for that PN, and it will give you a picture and cable length information if you want to match up another generic brand.
I bought mine through NAPA a couple years ago. They were from Bosch and exactly like the originals. Ferrari number: 146650 Bosch number: 0261200489 Bosch order number that NAPA used: 13240. Mine were $169 ea. at that time. Some other generic brands are available and will require splicing the plug on the wiring but they're much cheaper. Bosch website www.boschusa.com shows what they make for the 512TR. Another website to find generic sensors is http://oxygensensors.com Ron
