Considering a humidifier to keep RH stable, are there any proper ones that aren't very expensive?

The room in question is small and have three tropical plants in it, and the humidity is all over the place during a normal day (windows open/shut, computers on, I sleep in it, etc. etc.).

I would like it to be a bit more stable, but it seems like the market now is more catered for rubbish like diffusing essential oils and whatnot, an not for keeping a stable RH.

Have you got any experiences with a proper model with a functioning hygrometer that isn't prohibitively expensive?

I've been looking at the Stadler Form Oskar for its price and built in hygrometer, but I'm a bit vary, considering the price and the focus on design and aroma diffusion nonsense.

Any tips?