I just stack them on their sides in my garage. I lay a piece of cardboard on the ground first. What benefit do the stands give?
If they can't take the weight of up to 3 other tires sitting on them, how would they handle cornering? Bags are not necessary. I think the intent of the plastic bags is to keep the inside of the car clean after the tires are swapped, when you take your tires home.
A friend of mine, mounts them on his garage wall to keep them out of the way.
If you are buying rims for the winter tires, the rims on the summer tires stay on the tires
As for costs, you will have to factor in mounting and balancing, and the inconvience of having them done. Then again if you are thinking of it now, you can most certainly beat the crowds.
Also, will you be mounting them to the car yourself, or taking them in?
Also the generic Crappy tire rims, may not be hubcentric. (ie the hole in the middle of the rim is slightly bigger than the hub on the car. The rammifications of this are that you have to tighten the lug nuts carefully, making sure all 4 or 5 are centered so that rim is centered). I believe Tire Trends will sell you the correct hubcentric rim, but don't quote me on that as I have never used them.