Why did you use the conjunction 'but'? You're supporting my point, so...
... I thought you were being sarcastic... lol
hazards of text based communication. There's no inflection to indicate *sarcasm*
At any rate, yes it is expensive upkeep, but it could also become an extremely large creature if you have a lot of scrap.
This way, you cant spam large creatures for low cost without them dropping off rapidly.