First of all, a weight gainer is really nothing more than protein powder and sugar. There's really nothing "unnatural" about it.
Second, you need to start tracking what you eat each day on
Fitday. Your basal metabolic rate (BMR) is the number of calories you would need to eat in one day to maintain your current weight. You can find an estimate for that here:
BMR Calculator
Make sure to click on the "Daily Caloric Needs" link to get a more accurate estimate that takes into account your activity levels.
Once you have this number, eat that many calories each day for a week, and weigh yourself first thing each morning. If at the end of the week you have not gained a pound, then add 200 calories to your daily total and eat that number each day of the next week. Repeat this process until you are consistently gaining about 0.5-1 lb./week. If you are gaining faster than that, you might want to back off a little bit on the calories, as you don't want to gain any unnecessary fat.
jae215 gave a good example of a relatively quick, inexpensive, and healthy meal that is easy to prepare and will yield a lot of calories. It does cost more than $0.47 though. A single scoop of whey protein will cost at least that much.
For other ideas of what to eat, see this thread:
What A Bodybuilder Eats
I would recommend dividing your food intake across 6 meals spread out during the day. I would also recommend you get 1-1.5g protein/lb. bodyweight, 0.5g healthy fat/lb. body weight, and the rest can be whatever combination of carbs, fat, and protein you want.
BTW, did you do a search before posting this? The "how do I gain weight" question seems to be posted here every week. I am in favor of making a sticky for it. I answered the question enough times in the past that I could piece together a decent post from ones I have made in the past.
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