The Samsung Gear 360 is the most affordable 4k 360 camera right now (around $350 to $400 on eBay), but it is compatible only with the latest flagship Samsung smartphone (Galaxy S6 and above). It does come with a desktop-based software, Cyberlink Action Director, for stitching photos and videos, but the software is for Windows only, and can also be a little picky with older graphics cards. It is possible to use the Gear 360 without a compatible smartphone, but these restrictions make the Gear 360 harder to use for someone who uses a Mac and/or a non-compatible phone. Someone like Martin Smith.
The stitching process is not simple but fortunately gets easier eventually: