Iron, not as much stew as you might think. Getting 600-800 cals should be fairly simple. Plenty Potatoes and good meat and some bread with butter and you're looking fine. Remember that fats add calories quickly. Heck, make a side salad and use one tablespoon of oil in the dressing and you're looking at 120 cals added right there.
Crockpots vary in price. I really don't know what they go for.
A braise is just cooking in liquid over an extended period of time. Vindaloos, chili, stews, pot roast, tangines, adobos...they're all just braises, really, with a bit more liquid. A casserole is essentially a stew and a starch. Shepherds pie anyone?
The best thing about them is they keep well--they stand up to constant reheating. Make a huge batch and leave it in the fridge and you'll get good meals for a bit. As opposed, to say, stirfry.
Take something like chili--make it, serve it over/with potatoes, rice, pasta (cincinatti anyone?) add some cheese and some sour cream... You're looking at a quick meal with loads of calories. Or use some tortillas, etc. I think you get the idea.