HELP! New to ball pythons!! Humidity problem

It isn't completely impossible to control a UTH using only a lamp dimmer. It isn't very accurate, but as long as you check on it every day you should be fine. Obviously it isn't the best option out there but it will keep the temperature relatively stable.

The hydrofarm is a glorified dimmer. It does maintain the temperature within 3-5 degrees or so, but it has crazy temp swings and you need to set it much higher to get the desired temp. It works fine for my purposes though.

If you have the money, buy a herpstat. If you don't, save up your pennies!

The winter around here is stupidly dry, so I've had similar issues. Inside his enclosure, I moved the water dish so it was nearer to the 'hot' side so the water he didn't drink would evaporate. I also made the room that the enclosure was in less dry and that seemed to help a bit as well. (Live plants, humidifiers, bowls of water...)
Unused water will evaporate and make things less dry. I've heard that placing bowls of water around a room helps a room, so perhaps you can adapt that for use in the vivarium...?