Some things to consider:
A) Set repair to zero. If you're low on space, scrap the ruined units and rebuild, or send them off to die.
This avoids any whining 
about repair costing less
B) Have low repair. Give units zero maintenance. Give each component a negative resource generation ability.
(Now maintenance is proportional to the number of operational units, not the number of designed units)
To extend on this, you could make units free to build (or maybe 1 organics). How many troops you can support is another matter entirely.