For a camera lens, I can recommend a USB dew heater cable 80mm. Together with a little USB power bank the whole shebang sets you back less than a hundred bugs. The power bank has many applications such as charge your phone when off grid camping. The heater strips can be found here
https://www.amazon.com/Dew-Heater/s?k=Dew+Heater and a suitable 20,000mAh LI battery with USB port you may already have.
The heater strip works also on a powered USB port, such as provided at home from your phone charger.