In addition to the containers, measuring cups and paper towels you will need there are dyes and chemicals necessary to do the dyeing.
Procion MX dyes are sold by several companies and most companies have their own color names and numbers. So, for instance the manufacturer color Red MX-5B is sold as #12 Light Red by Dharma and #305 Mixing Red by ProChem. Paula Burch has an excellent chart on her site that has the various names and numbers for the different dyes.
http://www.pburch.net/dyeing/FAQ/pureMXcolors.shtml
This chart will also show which dyes are "pure' colors and not mixes of two or more dye colors. For a moment here I'm going to digress and explain why this might be important.
Dyeing is both an art and a science and you may find yourself leaning more towards one aspect of it than the other. If you want to create predictable effects and create repeatable dye recipes you have to be very precise. The amount of dye powder, temperature of the water used, the 'hardness' of the water, and possibly even the phase of the moon will affect the dyeing process. (Okay I'm kidding about the phase of the moon...maybe.) If you want repeatable results you have to be able to repeat.
On the other hand, you can decide to create one of a kind pieces that you create in the moment and you don't care if you can reproduce precision is not necessary.
Obviously you can also be somewhere in the middle and learn a bit about what dyes are likely to produce what colors and hope for the results you expect while still being spontaneous.
If you are leaning more towards wanting to reproduce your results, you will want to work with the 'pure' dye powder colors because results with the mixed colors will be unpredictable. If you are fine with unpredictable results you will be able to use a wider variety of dye powders.
The price for the dye powders vary by color. Dharma's current prices vary between $2.95 to $5.95 for 2 ounces. So how much the dyes cost will depend a lot on which colors you purchase. (I don't work for Dharma, I just buy from them and thought this would give a good price estimate for people interested in dyeing.)
In another post I'll talk about exactly which dyes and how much to purchase to start out.
You will also need soda ash to change the PH and complete the dye process as I've mentioned in a previous post. Dharma currently sells soda ash or $1.69 for 1lb.
After you have completed the dyeing, Syntrapol is used in the wash to help remove excess dye. Synthrapol is currently selling for $4.09 for 16 oz. (Dharma also sells a non-toxic Syntrapol replacement called Professional Textile Detergent. This sells for $3.75.)
There are two other chemicals you will often see listed as necessary, Urea and salt. Depending on what you read, you may or may not choose to use them. Urea is used to basically make water wetter, it allows more dye to be dissolved in a smaller amount of water. Salt is used by some to increase the depth of color and patterning. I don't use either though I have experimented with urea and intend to do some experiments using salt.
In addition to the chemicals you will need cloth to dye. I'll talk next time about cloth.