I have a pellet stove that is controlled by a low-voltage thermostat
which switches the stove on and off to regulate the temperature in the
room.  The thermostat is a standard low-voltage thermostat (like most
everyone has to control the heat/air in their house) with a simple
two-wire on/off configuration (no fan switch, etc.)

I have found smoke detectors on the internet which have optional relay
mechanisms that turn devices (such as lights) on in the event of the
detection of smoke.  I am looking for the opposite.  I would like a
smoke detector that will shut off the stove (by breaking the
connection to the thermostat) when smoke is detected, until it is
manually reset.

My question is; is there a product I can buy that will do what I
require, if so where can I buy it (must be < $70).

A combination of products that would be reasonable for a person with
basic electronics skills to assemble would be acceptable, as long as
instructions are provided.  My price limit is $70 for everything
needed, and the size should not exceed that of two smoke detectors (I
don?t want an eye sore on my wall.)

The result should be a relay that cuts off (breaking the connection to
the thermostat) upon triggering of the smoke alarm, and does not cut
back on until a manual reset is performed.

Notes: The pellet stove is run off of small wood pellets that drop
into a burn-pot automatically from a ?hopper? full of pellets.  The
exhaust is forced through the burn pot and out a flue by a fan.  When
the thermostat switches on, pellets drop into the burn pot, and an
igniter ignites the pellets.  When the thermostat switches off, the
pellets are no longer dropped into the burn pot, but the exhaust fan
is kept running until the stove is completely cooled.

Cutting the thermostat connection is my preferred option because this
will keep the exhaust fan on the stove running until the fire in the
stove has died and the stove is cooled.

Switching back on is not an option because the stove will ignite again
once the smoke has disbursed enough for the detector to go off.