The Bushnell radar guns work OK for what you pay for them.You can find them on ebay pretty cheap....about $100 or so.I have one and for speeds under 100 mph it seems to work OK.It does seem to miss a lot of passes once you get up to 120 or above when clocking fast planes
The next step up costs about $650
pinolelst
The Bushnell works just fine for RC's. I've seen them for $89