you can get a voltage regulator for less than a £1, depends on how envolved you want to get into it, you can buy a prebuilt unit for a couple of ££ or you can look a little into electronics and come up with something like a L7805CV voltage regulator and fit that, the important thing is the current draw of the dash cam, its unlikely to be higher than 1A so a voltage regulator will do the trick, very tiny and can be hidden easily (might need a heatsink though)
personally it depends on the mood, sometimes I want to build and understand and other times I'm happy to use something prebuilt