I made mine myself aswell.
peltier: 14 euros
cooler: 12 euros Huge one for a pentium 2 or something
thermal paste: 6 euro
motor clamp: pit box
wiring: pit box
to get the best result try to find an as big as possible peltier with the most amounts of watts. mine is something like 25watts but actually its too little...
i chopped a tamiya motor cooler in 2 pieces and filled the gaps with some solder. not ideal but it was the only thing could do with this thing keeping the costs low. then i grinded it as flat as possible using sanding paper and a lot of my time getting it right.
nicely put on the thermal paste as it is realy important for the heat transfer!
a tiny drop of it is enough for the 9square cm's.
i used it on both sides of the peltier.
on the warm side its omportant that the alu CPU cooler is nice and huge. mine never gets hot at all just because its such big, like 35 celcius max...
put some insulating on the cold side! i used some kind of strange thin foam like something you can put around a copper pipe it has a shiny layer of alu and a 1mm layer of foam in it. put the foamside on the motor to get te best result. when i put this insulating on the outside of the clamps and on some left-over space on the peltier it got 10 degrees colder!
uhm, i temped @ -15 when it was 15 degrees outside..
i should mention that most of the motors magnets are attached to the can with glue that can become brittle when freezed. heard about guys popping their magnets out with their fingers after cooling to below 0..
i guess this kind of motor cooling would be ideal for BL motors as you directly freeze the copper wires and therefore lowering the internal resistance of the wires. i bought a BL set recently and will test the cooling asap
just my 2cents worth