I use one of my older GoPro Hero black 3+'s with a class 10 64gb SD card, 1080p at 60 fps. I may even add a second for rear coverage.
You definitely want a class 10 can as the higher read/write rates will allow for higher resolutions and framerates. And at least a 32gb. But they are so cheap now, that a 128gb is a great option. I know your trying to keep costs down so 32 or even 16 set for looped recording will work just fine for dash cam purposes. You could actually get a discount through some insurance companies. USAA gave me a discount, after all it benefits them greatly.
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