As someone who comes from a country where 'gas' is a shit load more expensive than the US because of tax I call utter bullshit. It costs about 20-40p to go to a supermarket, or at most a dollar in your US terms. Over here there's also a massive competition war going on at the moment between Tesco & Sainsbury's for local convenience stores which have a good percentage of your normal weekly shop if you were buying everything fresh.
I suspect that mom just preferred to serve up frozen shit. And bullshit again on stuff like TV dinners being cheaper than other foods, they're certainly not over here in the UK. A simple chilli or bolognese is much cheaper if you buy the raw ingredients than any processed foods.
I suspect the problem's more that Mom just doesn't know how to cook.
Also, it's hard to have time to cook when you're working two jobs.