We all have to live within our means and if buying frozen instead of fresh allows us to put food on our plates through the month, then that's what we must do.
This is also why reading labels is important. I just checked the bags of frozen vegetables in my freezer. The Birds Eye broccoli has one ingredient listed which is broccoli. The store brand bag of cauliflower only contains cauliflower. The Green Giant spinach contains spinach, water, and salt.
Looks good to me.