Eye Tracking on the cheap

Looking to give eye tracking a shot, to learn the order in which the content is viewed on a desktop page or a phone, as the user goes through a click-through prototype. Unless there's a better way, I'd either look for a recording of where the user is focusing or a heatmap of the whole session that I can overlay on a screen recording session.

So far I've looked at Tobii & Gazepoint, but they're either too expensive for my budget or not really available here in Europe, or both.

Because I'm doing this for a side project, I'm not worried about accuracy, so I'd use any of the non specialised devices I have access to: Samsung S9 & iPhone XR that have face unlock, and a MacBook Pro Retina 2015.

If all else fails, I'd consider buying a device under 100 EUR, if I could adapt it to desktop or mobile use.

I'd also like to hear about other setups you've used for eye tracking with a very modest budget.