Found a solution. LTC6101 high side current sense amplifier. HV version allows up to 100V and depending on resistor combination can use a very low value sense resistor thus wasting very little power.

Datasheet example: 0.1r cs, 100r rin 4.99K rout will give 4.99Vout @10A load.

http://cds.linear.com/docs/Datasheet/6101fg.pdf