Typically a Hotcan meal will cost £3.99

http://evaq8.co.uk/Hotcan.html

Individual supermarket meal cans will range from around £0.50 to £1.50 depending on the meal so these are a very very expensive to heat a tin of food when compred to using something like gelled alcohol fuel such as Sterno.

A more cost effective solution would be to put the wet contents of a normal food can into a Mylar resealable bag and use a standard Chemical heater such as the Trekmates Flameless Cook Super Power Refill Pack, which I find will heat the contents of two wet food tins (400gm) at the same time if placed in a larger mylar bag placed in a neoprene bag i.e. a small notebook PC cover for insulation. This would also reduce bulk and weight compared to the Hotcan especially if you were needing to carry multiple meals.

http://www.amazon.com/Mylar-Ziplock-Food-Storage-Bags/dp/B004WYTCEA

or use a standard Flameless Ration heater bag for a single 400 gm tin.

http://evaq8.co.uk/FLAMELESS-RATION-HEATER-Turns-A-Wet-Meal-Into-A-Self-Heating-Meal.html