Depends on how budget your budget is really. SV650 is a good bet and with a little suspension work make a cracking budget track bike. Bottom end your talking CB500's Also older bikes like SRAD 600's make a cracking bike and fuel brilliantly.
I think Oxford do one now for about £100 it's a thin circular tube which could be hidden most places.
I think Oxford do one now for about £190 it's a thin circular tube which could be hidden most places. http://www.helmetcity.co.uk/oxford-gps-tracker/?gclid=CNaFl8aCrsgCFYiE2wod1qcONQ
You can, apparently, build your own for less than 50 quid. http://www.fastbikesmag.com/fastbikes-forum/showthread.php?t=
No doesn't work for me either. Not sure what went wrong there. If you google motorbike tracker it's on there.