A wash is a liquid solution in which fermentation will take place. A wash is usually made in a vessel called a lauter tun. The basic requirements for a wash are that it contains sugars which yeast will be able to ferment, and nutrients to keep the yeast alive while fermentation is occuring. There is a wide variety of sugar sources that can be used. Each sugar source will impart a different flavour to the final distillate. Such as:
Molasses will make rum. Grain will make whisky. Blue Agave will make tequila. Apples will make applejack. Grapes will make brandy. Any wash (sugar, molasses, grain, etc) which will ferment can be used to make vodka.
Cost of wash
Of course your location will influence the cost of the starting ingredients in your wash, but there are some general trend. Usually washes that contain just refined sugar and a nutrient for the yeast are the cheapest to make. Next, washes made from grains are often slightly more expensive than sugar washes, however, grain washes often require a large amount of work (especially if you are malting your own barley or corn). Finally fruit washes are usually the most expensive wash to make. The noted exception if it is harvest time in a location with an abundent supply of the fruit (in which case the only cost may be that of yeast).
Sugar content in washes
Washes made from refined sugar can be made to have as high of a sugar content as the yeast will tolerate. Molasses washes often are limited to around 16% sugar (8% ABV final alcohol) due to other components other then the sugar in the molasses causing yeast distress. Grain washes can often be made up to around 30% sugar (15% ABV final alcohol). Fruit washes are often comparable to grain washes. For both grain and fruit washes, the maximum sugar content is also dependent on the grain or fruit that is used. Some grains contain much more sugar than other grains.