Be sure to check out Delfina's tails- http://delfinamermaid.com/ I saw a few of them at MerMania this year, and they truly are stunning for a fabric tail.

In my opinion, I suggest you get yourself a monofin first and work your way up from there. If you have never been in a monofin before, you are going to want to train in it, and understand how to swim in it before getting a tail. From what I have heard, SunTails, MagicTail, and Finfun also offer their monofins sans tail skin. Once you get used to it, you can invest in as many tail skins as you want.