The best advice I can give is: Get in contact with a commissioner of some sort, or if you know someone who deals with crafts, ask them for advice and give the whole making stuff a shot yourself. Cost though? You're on your own there I think - from what I remember of following my friends around Manchesters' craft shops, it's not necesarily the most cheap stuff, and that's even for the fun fur - discounting things like thread, sewing machine and stuffing that you may use. So yeah, just have a look around at crafts shops, the basic uh... "template" for a tail is pretty much a tube of fur stuffed and sewn from the end to the base (where it will hook onto a belt), where you should have two straps (Yup, sewn on), one for either side of the back belt loop. I'd suggest ribbon for that though, much cheaper, much easier to come by. If you have access to supplies at school, for example however, I suggest talking to them, try to get some stuff - I'm sure there will be some elasticated nylon hanging around, but I wouldn't use anything with a width more than 15cm.
Now, that's all for a furry tail though (Or, if you're looking at scaley, felt would look a bit better in that area), and a basic shape and possibly a single colour - I'd say, if you've got the supplies handy, or if you've got the spare cash, experiment and have fun with it, keep messing around with it and perhaps even make a hobby of it!
With fursona... go with whatever - it all depends on you. What do you think resembles you? What do you feel close to? What do you think is cool, majestic, cute, inspiring? I could put a ton of descriptive words in there, and I could go on about looking at yourself and thinking, "What do I see myself closer to?" and all that, but again - it all depends on you. You should set your own reasons for finding fursona, or your fursonas.