Hi Brad. This is not a simple question because there are many issues involved.
1) Many studies have shown that the amount of vitamin/mineral listed on the label of a supplement is NOT what is actually in the bottle. At the present time, you have no way of knowing the 'actual' content of a purchased supplement. You can only 'hope' the label reflects the actual level of ingredients.
2) Storage, processing, age, etc. of supplements can affect their potency. Again you have no way of knowing about these issues for a given brand. For example, is the cheap brand of vitamin C cheap because the company purchases a huge lot of it from the manufacturer (to get a 'good price') and has been storing it in a hot warehouse in Texas for the last two years? Age and heat damage many vitamins.
3) Many cheaper supplements contain sugars, preservatives, colorings, etc. that just are not 'appropriate' chemicals in a quality supplement.
4) Medical studies have shown that the cheaper forms of minerals found in most supplements (such as: zinc oxide, magnesium oxide, etc.) may not even be absorbed. The more expensive, quality supplements will contain amino acid 'chelates' of minerals that have been proven to be better absorbed (such as: magnesium citrate, or glycinate, or gluconate or malate, etc.)
5) You can purchase a new car for less than $10K or you can purchase a new car for $30k or more. Quality always costs more, and it is often worth paying for it, especially where your health is concerned.
6) Vitamin E in most cheap supplements is the synthetic form called dl-alpha-tocopherol (also called all-racemic alpha-tocopherol). Real vitamin E is d-alpha-tocopherol - plus 7 additional forms (called vitamers). The real stuff has benefits the synthetic form lacks and some studies even suggest the synthetic form interferes with the body's processing of the other, good forms, of vitamin E. Any supplement with the 'dl' form of vitamin E is 'the cheap stuff', should be avoided and is a sign that the manufacturer doesn't care about the true quality of their product.
7) Avoid any product that does not list the exact form of each vitamin or mineral. Products that just say "Vitamin E" or "Calcium" are hiding the fact that they are using the cheapest ingredients, which again may not be the best. It makes me wonder 'what else are they hiding?'.
Hope this was helpful. Talk to the people at your health food store. They are there to help you. Expect to pay about $1 per day for a quality multi-vitamin/mineral supplement ($30 for a one month supply). In April 2002 the Journal of the American Medical Association recommended the use of vitamin supplements for all adults because it may help reduce the risks for many common diseases (heart disease, cancer, brain degeneration, cataracts, etc.). Invest in your health by purchasing a supplement that works!
Hope this wasn't too long, and therefore was helpful for you. Best wishes.