The simplest or cheapest way would probably involve Kirlian Photography. This type of photography was invented by Semyon Davidovich Kirlian, of Armenian descent but born in Russia in the late 1800's. In the World War II era and post era, his trademark photography was accidentally developed (like most good inventions). Any picture you see in this article is an example of it.
Kirlian found out that if you place an object on a photographic plate and charge the plate with high voltage, you are left with an interesting picture which exposes the 'aura' of the object. Well, it's up for debate. Some would say it's simply bio-electric energy or other forms of electric energy that are seen. Others believe it is aura, or even the soul itself that is seen. There can be a common ground of concordance between the two. If you weren't inclined to believe Kirlian Photography exposes the soul, the only other way to see someone's aura would be to develop the ability within your own mind using esoteric techniques (lest you be born with the ability from the start.)
A common method to see auras is to focus on opening something called a Third Eye, in mysticism it resides in the middle of your forehead and is invisible itself. If you do open it though, you can gain insight into realms that normal sight cannot. There are countless articles out there, online or otherwise, that show you how to see someone's aura or open your Third Eye. It is not some guarded Brotherhood secret, very little digging is needed. There are many paths as well. The way I understand it, you must spend a lot of time meditating and becoming sensitive to the flow of energy in all things. When you feel this energy is real (usually you start by only imagining things like energy and supernatural sight are real), you control it with your intent to open your Third Eye, or some effect similar.
As with anything else, practice practice. You do need a certain degree of faith and imagination to get through the first few stages until you can feel the 'realness' of it all.
