We ran by Walmart tonight and I got their standard temperature / humidity gauge to test out for you guys. It was $8 I think for both a temperature and humidity reading, both digital. I'm not sure if $8 is too much for your budget, but it might be very well worth saving up for. Or ask for it for the keet's holiday present!
It's really helpful for the humans, never mind the keets

Humans need to be healthy too!
I'll post a review and photos as soon as I get a chance!