You can get a decent dual lens cam on ebay without breaking the bank. I have used one for nearly four years and it's done the job. One like these two should work.
http://www.ebay.com/itm/2-7-Inch-Vehicle-Dual-Lens-Rotate-180-Degree-Driving-Recorder-Car-Camera-F30-L0/292019317690?_trksid=p2047675.c100005.m1851&_trkparms=aid=222007&algo=SIC.MBE&ao=2&asc=41393&meid=a5152fa1d3b643fcbf9b0a3064b2a417&pid=100005&rk=3&rkt=6&sd=162103466204
http://www.ebay.com/itm/1080P-HD-2-7-Dual-Lens-Dash-Cam-Car-Video-Recorder-DVR-Camera-GPS-Logger-R310/222206323025?_trksid=p2047675.c100005.m1851&_trkparms=aid=222007&algo=SIC.MBE&ao=2&asc=41393&meid=a4b88414a62843edafa557a6aad74750&pid=100005&rk=6&rkt=6&mehot=pp&sd=401271778863
Or just install one app in a phone from android market.
https://play.google.com/store/apps/details?id=com.happyconz.blackbox
http://www.ebay.com/itm/2-7-Inch-Vehicle-Dual-Lens-Rotate-180-Degree-Driving-Recorder-Car-Camera-F30-L0/292019317690?_trksid=p2047675.c100005.m1851&_trkparms=aid=222007&algo=SIC.MBE&ao=2&asc=41393&meid=a5152fa1d3b643fcbf9b0a3064b2a417&pid=100005&rk=3&rkt=6&sd=162103466204
http://www.ebay.com/itm/1080P-HD-2-7-Dual-Lens-Dash-Cam-Car-Video-Recorder-DVR-Camera-GPS-Logger-R310/222206323025?_trksid=p2047675.c100005.m1851&_trkparms=aid=222007&algo=SIC.MBE&ao=2&asc=41393&meid=a4b88414a62843edafa557a6aad74750&pid=100005&rk=6&rkt=6&mehot=pp&sd=401271778863
Or just install one app in a phone from android market.
https://play.google.com/store/apps/details?id=com.happyconz.blackbox