I just use a cheap VPS like Vultr [2] to terminate persistent ssh tunnels from the cameras and run a self-signed https gateway into them. It's under $5/mo for the cheapest VPS option.
It's a bit of work to get it set up, but nothing crazy hard if you know your way around something resembling a LAMP stack and ssh tunnels. There's no third parties integrated so you control the data and have a lot fewer privacy/safety concerns in general.
If there's no wifi available, at&t offers mobile hotspot prepay service for as low as $25/mo.
[0] https://www.adafruit.com/product/3414