sure he tells you the motor is locked up but he has a pump to swap the motor.
A pump motor is typically a constant RPM engine not designed for variable throttle..so its not even an ideal application.
After you swap it. Which isnt exactly an easy task.
Then he doesnt have a radiator and that is an out of production part so you are going custom industrial radiator. Count on a grand and probably 4-6 weeks.
Since the motor is bad you cant test the transmission or hydraulics. Any problem with either would be disastrous.
In good operating condition given the age and size etc thats a maybe $10k machine. Id bet youd be $15k into it before you moved the first pile of dirt.
That said if you are an equipment mechanic, have all the tools and equipment can do all the work yourself and have all the free time...you might break even.