the only place you can buy the detector and get the full warranty is through valentine 1 directly.
check out valentine1.com there is a bunch of info on the detector and ordering info as well. i think it will end up being about 450 shipped with the detector and the "concealed" display setup. if you wanted you can get a rear-view mirror for the e39 that has it built in or you could even have it on your message bar on the gauge area. both of those setups are available at beastpower.com
great website for all e39 stuff as well. i bought my SPEC stage 3 clutch and JBRacing lightweight flywheel from them. Best upgrade for my car so far i think.