As GodDog said, you cannot get 250 in one play through. Also, the cranes are only saved once you finish a chapter, not at checkpoints like style points.
However, once you have finished the game, you can use the chapters option from the main screen to re-visit the Mega Battle level at the end of chapter 3 over and over.
There are 5 or 6 cranes on this level and if you do it on casual, it's easy to kill Lok with 3 barrage attacks in a minute or two, ending the chapter and saving the cranes you've collected.
My route around this level when boosting was:
1. Hit Lok with a barrage as soon as you come out of the lift, triggering the first cut scene 'Have you seen my toy?'
2. Run around the outside of the room picking up the cranes. Remember to grab the one in the middle area near Lok.
3. Hit Lok with another barrage while moving to one of the staircases. This will trigger the penultimate cut scene, 'Do you like Pineapples?'
4. Run up the stairs and grab the last crane and health if required, then go back down and finish off Lok with another barrage.
5. Skip the cut scene, wait for the end of chapter summary and auto save. If you've got 250 cranes the achieve will unlock at this point. If not, go back to the main menu and repeat the steps above until it does.
It does take a while if, like me, you didn't grab that many cranes through the campaign, but it will unlock eventually.