Well shit, I'll just retype it. Here is my take on the matter from being in the iron game for over a decade now. IMO, the best, most effective supplements are ALSO the cheapest.
Multivitamins are kind of the baseline. Most people don't eat a wide enough variety of foods to get all of the vitamins that are included in these. They are also super cheap, especially if you get them on sale like I do, $10 or so gets you about a few months worth. You can also get the individual vitamins and minerals (the vitamin C tabs, vitamin D, or whatever) if you want, but a multivitamin covers most of your bases.
The next thing I think everyone should be taking is fish oil. Too many benefits to talk about, but if you want to read more about them, google 'oil of pisces' and go to that website. Fish oils are just a good cheap way to get some essential fatty acids. Again, get them on sale like your multivitamins, and you can get a couple months worth for about $10. I take 6 tablets a day.
Third, especially if you are a weightlifter or other kind of athlete, is creatine. a 500g jar of creatine monohydrate (the only kind you need) can last you several months at 5g a day, and costs about $15 or so. Again, don't get those super expensive creatines like Cellmass or whatever weird names they have, which cost $50 and have a ton of ingredients, just get the active ingredient (creatine monohydrate). Now a word about creatine, I remember maybe 10 years ago when the hysterical media and soccer moms were flipping out about creatine, saying it was basically a steroid and should be illegal; this is bogus. Here is a Barney-style breakdown of what creatine does, in case someone doesn't know. Muscles run on ATP. ATP only last for a couple seconds of muscle contractions, so it is constantly being replenished. It is replenished by phosphocreatine stores in the body. With exercise, you can increase the amount of phosphocreatine available, this is how you increase the amount of pushups you can do in 2 minutes with a consistent routine; you are causing your body to increase its phosphocreatine stores. Creatine simply adds to the amount of phosphocreatine available to the muscle. It also recently has been shown to have more beneficial effects, but the main thing it does is to allow you to exercise harder for longer.
Next, for people trying to lose fat, is ephedrine. Another one mired in controversy, but people have been using ephedrine (the pharmaceutical grade version of ephedra, which comes from a plant) for thousands of years. It is available at every pharmacy I've been to (it's just behind hte counter now, because you can make various illegal drugs out of it) for about $12 for a months supply, at 3 pills a day. You might remember the media scare related to ephedrine a few years ago, when Kory Stringer, a lineman for the MN Vikings, and a pitcher for the Baltimore Orioles, died "because of complications from ephedrine".... never mind that they both took many times the standard dose, hadn't eaten, and were working out in extreme heat and humidity, and were both out of shape. Anyways, taking a standard dose (20-25mg ephedrine, 200mg caffeine) is safer than most common drugs people take every day (aspirin, ibuprofen, etc) in terms of mortality rates.
So there you have it, my take on the cheapest and most effective supplements available.
Multivitamin
Fish oil
Creatine monohydrate
Ephedrine
Don't waste your money on supplements that CONTAIN these ingredients, but ALSO have a bunch of other stuff in them and cost 10x as much: these are the ones doing the work. Hope this helps.