It does sound rather a high voltage, but remember the higher the voltage the lower the current and thus the thinner the
wires need to be back to the controller (which allows for longer and more flexible cable runs - remember in an industrial
production line you might have hundreds of motors and kilometres of wire!
Motor controllers for that voltage will tend to be industrial units (robotics tends to stick to 12/24V) which will be more
expensive (again they are designed to be reliable for decades in a factory environment and bomb-proof costs money).
Perhaps this is a case where the open-source motor controller project is appropriate: http://www.robotpower.com/products/osmc_info.html
(Only good to 50V that version, but join the yahoo group if you want more info http://tech.groups.yahoo.com/group/osmc/
The encoder might run at a higher voltage of course (common for industrial units). What current is it taking at 5V on the V+ pin?