Yeah public domain is good enough for me. But I should add that there are huge differences in the wayclassical music can be interpretated. The cheap cd's are either very old recordings of not so hot orchestras or conductors or new recordings by run of the mill, competent musicians. Some labels have their own house orchestra that bangs out numerous works and puts lots of titles onto their label.
True classical music affectionados (sp?) get really excited by the conductor, who can really influence the dynamics and sound of a piece. Or maybe the appearance of a noted soloist. But for the average listener, who isn't comparing one recording over the other, the cheap recordings are great.
I don't know for sure, but a handful of classically trained musicians and 256 track studio recording devices...it wouldn't be too hard to make 1 or 2 violins sound like 16. Do everything in one take, fix up the errors digitally. could be pretty cost effective.