Unfixed cat??

I have 2 cats, 1 I've had since she was 5 weeks old and the other I've had since last October and she is a rescue from the shelter. She came fixed. The one I've had since infancy is not fix. They are both strictly inside cats and never go outside. No male cats are in my home and I've trapped all the male's that were coming around and took them to the shelter. I haven't heard a male cat in months and both my girls have no desire to go outside. They want to charge me a ton of money to fix her and I just can't do it right now. Am I a bad owner for putting it off for a while or not doing it at all? I make sure they don't ever have a chance to breed. I also have to fix my female dog. They want almost $600 to fix them both...