Ive seen uth controllers pop up on google shopping for about $10. Doesn't get better than that. Remember: dimmers are unreliable and most of them will immediatly half your uth's heating ability. I also suggest attaching one to the side of your enclosure to greatly reduce the need for using lights to provide heat(it just eats humidity with lights only). Untamed uth's can spike 150f reeeeeal fast like.

To help temps, even taping/wrapping an old blanket or towel around 2/3 sides will help for now.

We actually threw the screen top away and made a taller(12in), mostly solid lid for our 40. Even before i swapped to natural planted it greatly helped humidity. Tin foil and other remedies do help minimally, but on an extreme tight budget, youll fast learn to be a diy guy and recycle almost everything you see to help your cause till ya get it right.

Can you post a pic of your setup so far?