You don't need all the fancy cleaners just some Dawn dish soap and a brush with a good blast from a bottle cleaner to clear the soap works fine when they start to crud up. Get the water as hot as you can stand it and save a few bucks.
I depends upon the nature of the gunk you are trying to get rid of and how much effort you want to put in. Dish soap only contains dispersants and surfactants, which means that once the gunk has been lifted from the surface they can take it away, but they aren't good at lifting the gunk in the first place (which is why you need to scrub the surfaces). What makes the fancy cleansers fancy is that they have stuff in it like sodium percarbonate which goes right after the organic gunk. If you want to go cheap, you can go with powdered dishwasher detergent or a generic brand of Oxiclean (or Straight-A or One-Step, etc.), but those would have different percentages of percarbonates and such in them which means you'd need to use a bit more than you would with PBW or Oxiclean, or you need to soak it a bit longer. Bleach is another inexpensive option, but you want to make sure you are using it correctly so that it is effective and safe to you and your brewing equipment. You won't get rid of organic films with dish soap without a heck of a lot of scrubbing, and if you have mineral deposits, that is a whole different beast to attack.
One of the early Brew Strong episodes had a great interview with Charlie Tally of Five Star Chemicals. He did a really good job talking about all of the different kinds of cleaners and how best to use them. He covered the best ways to use bleach very well in either that episode, or one that I recall from Basic Brewing Radio.