The tools of the casting are an aid to focus. By training yourself that a green candle does "X" and a red candle does "Y", you are training your focus to be on task "X" when you light a green candle and on task "Y" when you light a red one.
You could just as easily do "X" and "Y" without the candles, but it is a focus for you.
So yes, you can dedicate some cheap candle holders to specific tasks and then buy them once and as you say use the cheap, plain white tea candles. You would get much the same effect.
To further supplement, you can also take multiple sets of them and decorate them in a fashion that illustrates the purpose. For example blue is for healing, truth, inspiration, higher wisdom, occult power and psychic protection, understanding, good health and the feminine principle in Nature.
So you could have one blue one marked with a rune, Tolkien's Elvish Script, Theban, or whatever to be the one you use for healing and have another blue marked for inspiration.
Also you can get some herbs or herbal oil extracts that are complimentary to the task at hand and anoint the holders to further enhance what you are doing.
Remember that the tools and trappings, while are nice and can really help you feel your connection, are not as important as the ritual and your mindset is. So go ahead and go witchy on a budget. The Powers that Be aren't going to pull a Simon Cowell on you and rip in to you for not having the right shade of blue on the table.