There is nothing wrong with protein shakes, but they don't magically make you gain muscle and do cost money. I would work out and build muscle eating regular food first, and if you stick to it, switch over to protein shakes if you've been monitoring your diet and you are sure you aren't getting enough protein.

You can buy whey/casein (1, the other, or both mixed) protein and mix it in some water and you are good to go. They also have it mixed with various flavors if you don't like drinking it straight. Buy whatever tastes best to you and is in your price range. It is hard to get to 1-2g of protein per pound of body weight without taking protein shakes unless you love meat and nuts, so use whatever you like. I'm not weight training yet, but I only manage to eat 90g of protein in a day, so when I start lifting I'll probaby get a protein shake of some kind (note, 1g/lb is the low end on recommended, while 2g/lb is the very high end on recomended while trying to build muscle)

P90x. Its actually a totally legit fitness regimen. It doesn't take a lot of money, you don't even need weights, just exercise bands and room to do the exercises. I suggest getting some type of protein like whey.

wait, how can you be skinny with a little bit of flab? Youre either slim or flabby lol choose!

I can vouch for P90x, haven't used it but I know people that have.

Calisthenics are a good inexpensive way to build muscle and increase definition of your muscles but they're (typically) a pretty boring way to workout and most people need to be pretty dedicated to accomplish anything with them. For a skinny guy most forms of physical excercise that are challenging enough will create noticeable improvements in your appearance, and it is (probably) better for you to choose a handful of activities you enjoy doing than to focus on a dedicated regime and to change your lifestyle.

nice topic. (yeah I'm just bookmarking for future reference)