To quote the manual:
The SDI port of your camera outputs uncompressed 4:2:2 10-bit HD1080 video while recording live with the camera. Make sure the SDI Overlays are set to Off in the camera's display settings to avoid the SDI output showing action safe and title safe frame guides as well as the camera status strip.
You can capture the HD-SDI video output from the camera with any HD-SDI capture hardware, and with any video software supported by your capture hardware on Mac OS X, Windows or Linux. Each of these applications have their own project preferences that let you capture the video in an uncompressed or compressed video format of your choice.
You could also record the HD-SDI video output to a traditional tape deck or to a HyperDeck SSD recorder for a redundant and portable backup of your recording. When the camera is set to record 25p or 29.97p and SDI overlays are switched off, the SDI output will be 1080i50 and 1080i59.94 respectively.
Long story short... if you already have the hardware to capture a uncompressed 4:2:2 10-bit HD1080 signal via SDI - then you could definitely do this to cut down on SSD costs.
Another option if you have a Mac or PC with Thunderbolt is to capture via Thunderbolt to Blackmagic Media Express. Again, this is all documented in the manual.
Having said all this though - if you only have a tiny budget, and more time than money, then just get a small SSD, and dump the footage more regularly.
Happy shooting!