Zalman ZM-K650-WP Keyboard @ techPowerUp
 

The Z-Machine K650WP from Zalman is a membrane keyboard that comes in at a price point where there is really no competition from branded mechanical keyboards. At the same time, it offers a waterproof design, dedicated volume-control buttons, and an internal aluminum plate for structural rigidity, making it great value for the money.

https://www.techpowerup.com/reviews/Zalman/ZM-K650WP/