I've done a lot of research on this. If you buy new the package will save you money. If you buy used you don't really have a choice, but to buy the tires seperately. If you buy wheels it's going to cost around $50 to ship, plus $50 for tires if bought seperately. Then you have to get the tires mounted/balanced.
Where I live that's at least $20 a wheel if you can find someone willing to touch the rims. Most places don't want to be liable cause if they scratch them they know your going to raise hell.
When I bought my package it was $50 total for the shipping.
I saved money on the tires, shipping, mounting, balancing, and they threw in new lugnuts. Plus they did an excellent job mounting them, (no scratches). You can save $100-$200 in the long run. When my tires wear out, i'm going to just buy a new package and sell the old rims. I mean by the time I order tires, have them shipped, mounted etc... I could throw an extra $300 in, and have new rims. I could sell my old ones for that, and no hassle finding someone to mount them without scratching them.