If the windows dont have trickle vents what is the less than 5k solution besides running a dehumidifier 24/7?
Retrofit trickle vents if you can, otherwise experiment with leaving the window just cracked open.
I'd also experiment with heating the room selectively to see if that solves the issue. You can do this with something as simple as a TRV fitted to the radiator in the room, a stand alone electric heater or as expensive / complex as installing 'smart' heating like Tado that offers room by room temperature control. You might find that trickle vents and a slightly warmer room makes the issue go away. If it doesn't then you need to figure out where all the excess moisture is coming from and how it is making it to that location.
Retrofit trickle vents if you can, otherwise experiment with leaving the window just cracked open.
I'd also experiment with heating the room selectively to see if that solves the issue. You can do this with something as simple as a TRV fitted to the radiator in the room, a stand alone electric heater or as expensive / complex as installing 'smart' heating like Tado that offers room by room temperature control. You might find that trickle vents and a slightly warmer room makes the issue go away. If it doesn't then you need to figure out where all the excess moisture is coming from and how it is making it to that location.
FWIW the last month has been bonkers humid.