Thanks to everyone. I am changing my mind a little bit. I have decided
that I can do without a thermostat if no cheap one can be found. I
would simply use a portable electric stove and would adjust heat
setting depending on ambient temperature. There is a couple of
thermostats on sale on ebay, if I can win them for a sensible price, I
would use them, otherwise, I am not interested.
I am also thinking whether it would be sensible to use a little fan to
move air inside the enclosure. I have a shitload of 10-30 watt fans,
including ones with little if any plastic, and could easily wire one
up inside the enclosure, to distribute smoke and especially
temperature more evenly. OTOH, perhaps this is unnecessary. In any
case, the cost of the fan is zero.