In our analysis, some of the meals that best met these criteria were Wattie's snack frozen meals, which the Herald on Sunday was able to buy from Countdown for $3, on special.
The Wattie's options the Herald on Sunday looked at, including beef lasagne, fish pie and chilli con carne, had between 1,070kJ and 1,140kJ of energy and 11.8g and 15g of fat.
They were in the middle of the range for sodium, at about 500mg per serve.
Other options, such as Wishbone's beef lasagne, which Turnbull said many people chose thinking it was a fresher, healthier option, had three times the kilojoules for a serving that was one-third bigger.
Dakshin lamb korma, with a regular price of $5.19 at the supermarket, packed the biggest punch for its 300g size, with more than 40g of fat and almost 3,000kJ.
The biggest problem with many ready-made meals, for your wallet and your waistline, was that they are not as big as a standard meal.
Most of the meals surveyed were between 270g and 320g, although the Wishbone options were 450g. Turnbull sais many were not satisfying as a main meal.
"Compared to what they normally eat, people are still hungry. If you have one that's smaller than normal you might be tempted to eat a bag of biscuits afterwards."
She recommended supplementing them with inexpensive options such as a leafy salad or frozen vegetables.
Deli-style meals, such as Wishbone's, were fresher and nicer choices, Turnbull said, but people needed to be aware they were eating restaurant levels of calories and fat.
She said people should be clear that the convenience was costing when they bought heat-and-eat meals. In most cases, you could make the same meals more cheaply by buying the ingredients and cooking from scratch.
"If you're regularly needing to buy ready-meals, you need to ask [yourself] could you do double-batch cooking? It doesn't take long to make a chilli."
People should also be careful about meals that were branded "healthy" or carried a name such as Weight Watchers, she said.
"In many cases when you look at special diet products they're often not, it doesn't necessarily make them a healthy choice. You need to look at them all independently.
"You can't say that one will be a better option because it's Weight Watchers recommended."
In our analysis, Weight Watchers came in behind Wattie's meals and a couple of slices of a McCain frozen vegetarian pizza.
The best choices in terms of fat and energy were chilled soups. Turnbull said they were good because they had a high vegetable content. But they were high in sodium, second only to the Wishbone meals and a Dakshin lamb korma.
Turnbull said some would find soup was enough dinner if they'd had a decent lunch. "But you're likely to need maybe some wholegrain toast and cottage cheese or something to make it more nutritionally complete."