Yea buying online is almost abut the same as making it yourself but making it yourself is still way cheaper than the LHBS
I went for a stainless 50' chiller cause I didn't like the fact that copper oxidizes and didn't want oxidation coming off in my wort, but I doubt it is really much of an issue, plus I couldn't bend stainless myself nearly as easily so it seemed more worth while. Copper does conduct heat faster I suppose although either material will work for this.
My hardware store only had 3/8th inch coil in 20 foot lengths, and 20 feet just isn't really enough. I thought it would be enough for my pre-chiller (made the coil smaller by wrapping it around a conrey keg), but I have my doubts.. It only drops the tap water temp about 5-6 degrees so I end up with about 76-77 tap water for cooling this time of year..I think a longer coil might have worked better.