@Aleksander,
Have you considered buying a used fire fighting thermal camera ? I bought several for prices between GBP30 ($45) and GBP200 ($300). Most need some TLC due to a hard life but the good points are that they are often just a small aluminium chassis inside a larger heat and water proof case

I have several ISG Talisman Wasps that are built in this way. Once you remove the bulky case and non essential parts they come down to the compact BST head and a couple of small PCB's. Now the really good news...non tube based Fire fighting cameras are usually at least 320x240 resolution with 30 or 60 fps refresh rate

They usually have decent Germanium optics as well !
As a bonus, most have both internal video displays AND composite video output on an external socket. The Talisman series and many others also offer an option for a 1.3GHz or 2.4GHz long range video transmitter for communication back to a command and control centre at an incident. I have not checked to see if that option is fitted in my units but it is easily added anyway. My Talisman Wasps also include a X2 electronic zoom function activated by a simple button press.
The joy of fire fighting thermal cameras is that they are well designed with fully automatic operation and most of the features needed for a Drone deployment

Have a look at your local auction sites and see if you can find yourself a bargain. Be careful buying off eb*y as some of the fire fighter cameras sell for silly prices and if they do not work you take a risk of wasting your money. I repair them for fun so that issue was not a problem for me. You may wish to ensure the camera actually works before buying. Avoid a Pyro Vidicon based camera like the EEV ARGUS 1 (Yellow Case) as its internals are too bulky and sensitivity is lower than the later BST based cameras such as the ARGUS 2 (Black case) Even the ARGIS 2 is a little bulky inside. Look for an ISG Talisman Wasp or Elite if you can finds one. Avoid the pyro Vidicon standard Talisman for the same reasons as the ARGUS 1.
Final comment... most of the 320x24 pixel 30 and 60 fps fire fighter cameras are subject to ITAR regulations so be careful if trying to export out of the USA.