I started with a 40cu bottle of C25 and when it ran out I traded it up to an 80cu bottle to make it last longer. They gave me 100% credit for the smaller bottle towards the bigger one and by breaking it up it lightened the load on my wallet a little. There's so much you need to buy when you first start doing it every little bit helps. What's funny is that refills for the 80cu are actually less than the 40cu at my local Airgas. I think it was $30 something for the 40 and the 80 is only like $27. The 80cu is a good size for my cart and seems to last me long enough. Sorry I don't remember what the bottles cost but I do know the 80 was about a hundred bucks more than the 40.
Go to the Lincoln Welding Foundation and order a few boxes of welding coupons. They have a metal project kit that has some 1/4" and some 1/8" cold rolled steel coupons in it that are great for practicing. You get a break for the more your order and you save a little on shipping too. I think I got 5 kits when I ordered and it came to about 50 bucks including shipping. There's no mill scale on it and you can weld on it right out of the box. I still have about half of it out in the garage. It's been good for the welder and also good to play with on the plasma cutter I bought. See if this link works:
http://www.jflfoundation.com/ProductDetails.asp?ProductCode=METAL
I also have the HF table and it's been well worth the money. I cut a little notch on the backside so the working clamp would clamp flat to it to make sure I got a good ground. I also have a little wad of copper from some old power cable I put under the clamp to maximize the ground too. That's a tip I got from Jody ala Welding Tips and Tricks on youtube which leads me to my next tip. Watch his series on MIG basics and you'll learn everything from grounding to how to set tension and much more. Here's a link to the first video in the series. He's great and his videos are very informative.
http://www.weldingtipsandtricks.com/mig-welding-basics.html
I also have one of the HF blankets too. Just remember it is fire resistant but not burn proof. I threw over my legs the first time I used it and the sparks burned right through it. Now I throw it on the floor to keep it from getting burn spots all over it. It's handy to have but not what I thought it was. lol
Never, ever use brake cleaner to clean parts before you weld. It can kill you. Do a search to learn more. Just don't do it.
I'll post again when I think of more.
I've fit up to 3x 125cf cylinders in my 4 door econo box trunk.Although the back seat folds down which helps. Weld shop won't help me load due to liability. They roll it right to my car but I have to load it. 
