If it's just the connector that holds the bulb itself that broke, it's a fairly standardized part called a 'tombstone' and costs <$5 at any local hardware store. Replacing it should be even less work than replacing the entire fixture.
For best efficiency you totally remove the ballast and wire the tombstones at one end (new ones included) straight to 120V.
Note: for either of the above solutions, you may think that just turning off the light switch is safe enough, but the yutz that wired the fixture might have put the switch on the neutral line instead of the hot, which makes it basically impossible to remove / install a bulb without shorting it to the frame, much less rewire the fixture. So just flip the breaker no matter what you are doing.
Are the fixtures using T12 bulbs, or T8? I may have close to an entire case of them I'd rather donate and continue my LED conversion project.