TomTop offers this 4K WiFi Waterproof Action Camera in several colors (Yellow pictured) for $27.99 with free shipping. That's $7 under our mention from last May and the lowest price we've seen. (It's the best deal now by $17, outside of the mention below.) Features include a 2" LCD, up to 4K video recording at 30fps, 16-megapixel photo resolution, 170° wide-angle lens, WiFi, USB, microSD card slot, rechargeable Li-ion battery, and housing that's waterproof up to 98 feet. It comes with multiple mounting options.

A close price: Bluebetter via eBay has it for $28.99 with free shipping.