[stuart]

least expensive i'v seen is hk's...

Hobbyking Mini GPS Data Logger SKU: 9340000001$71.99 WEIGHT : 35g | BACKORDER


if you have an android or smartphone you can down load th rcspeedo app whiich will hear your loud speed planes passing and doppler the speed. if you do try the gps devise i ask you to please post you findings here at wattflyer. i would be very interested in what you find. there is another devise like hk's gps devise but it costs more.