Naturally the most cost-effective is buying a bale of good peat moss and a large bag of perlite and mixing your own. Do not buy Miracle-Gro stuff nor anything that has fertilizer in it! You will have to pick a bale up locally (HomeDepot, Lowes), but you will have to order a large bag of perlite online from somewhere. It really depends on how much potting mix you want or need to get. If you have room to store it, and you intend on staying with the hobby for a long time then the larger portions are far better choices economically. You can also adjust the ratios a bit for the varied types of plants...but, they all will be ok in a 50/50 peat and perlite mix.
There are vendors online (Amazon, eBay, Walmart, etc.) that sell pre-mixed "carnivorous plant soil"...some are ok some are not. Sometimes the quality varies. It's kind of a crapshoot. Ready-mixed CP soil bought from well known carnivorous plant sellers *should* be good. The grow mix that the FlytrapStore (sponsor of this forum) sells apparently is a very good mix, and though a little pricey it does include shipping (I think
As an alternative, to the readymix but still in small volume you could go with a small bag each of perlite and peat moss:
Hoffman 10 qt peat moss on Amazon @ $20
Harris 8qt perlite on Amazon @ $16
That would give you basically four gallons of 50/50 grow-mix with a 1/2 gallon of peat moss left over. You could use the left over for a top dressing to cover the perlite (but the perlite *will* find it's way to the surface) or maybe for a seedbed on top of a pot of the regular grow-mix.
Naturally, you could substitute some dried Better-Gro sphagnum moss for the peat moss at a bit more expense. Things see to usually do better in it. If nothing else, you don't have the issue of excess humic acid and tannins present that can be a problem sometimes.
As for pots for the flytraps. It's usually stated to use plastic pots and (second choice) well-glazed ceramic pots. Terracotta, clay, stone, etc., pots that can leach minerals into the growing medium should be avoided. Flytraps have long roots so 6" deep pots are usually the minimum depth recommended. Big, 32oz plastic cups can work though regular plastic pots of the right height will be wider at the base and thus more stable. Plenty of drain/wicking holes should be in the bottom of the pots/cups. I usually add a few extra holes just above the bottom on the sides...in case the pot sits flat against the bottom of the tray/saucer the side holes allow free water movement.
Best wishes and welcome to the forum! Don't forget to check out the seed bank!
ETA: What Evenwind said about the info on the Flytrapstore website and here on the forum...I had just already typed this when I saw his post!