The Bakeey GTX is a new smartwatch that is not only affordable but also packs multiple features. According to the manufacturer, the GTX supports heart rate, blood pressure and blood oxygen levels monitoring. The Bakeey GTX retails for as little as US$27.99 and is compatible with Android 4.4 and iOS 9.0 or newer.
https://www.notebookcheck.net/Bakeey-GTX-A-sub-US-30-smartwatch-that-supports-sleep-tracking-and-can-monitor-heart-rates-blood-pressure-and-blood-oxygen-levels.481608.0.html