I have a PAJ Trackers on the MG, Morgan and Harley. https://www.paj-gps.co.uk/

Internal battery so I have to charge every couple of months or so, but they still work if the battery is disconnected. Mag mount so fairly easy to hide.

Subcriptions are between £6 and £10 per month. There are cheaper out there - Sino Trak is also good and just relies on a SIM card and PAYG subscription

"Y mae dafad ddu ym mhob praidd"
1972 4/4, 1981 MGBGT, 1984 FLHT1340, 1980 XLH1000, 1990 ZX10