I'm down with whey protein. It's fairly cheap, quick, easy, and it is a high quality source of complete protein.
I usually avoid weight gainers. If you want a calorie dense meal that's quick and easy to consume, then just make your own weight gainer shakes. Use milk, whey, fruit, healthy oils, oats, peanut butter, or whatever you would like and toss it in a blender. Voila, a cheap and healthy alternative to that sugary crap.