Cheapo Zumo car unit, stuck in a cheapo w/proof cover or otterbox, or tucked away so it can't get wet.
This one cost me £13 quid from Ebay......
If I wanted a cheap 'Proper' bike GPS that will do PC based planning blah blah blah, I'd get a Quest (version 1, not the crappy V2) with a ram mount and power pack , all in for 100 quid or less off ebay
For general running around the streets, going to a street location etc though, my cheapo disposable Zumo is more than adequate