IMO, sand is much better, but again, JMO
If you are going to switch, now is definitely the time to do it. It will probably restart your cycle, but now would be much much easier than later on. And waiting ti l you cycle completely will not save you any work, bc cycling actually affects the surfaces more than the water as far as growht goes, indirectly affecting water quality.
And replace it all. If you can get southdown, or another aragonite type sand, from a source other than an LFS, it will more than likely be int the 50lbs for 5to10 dollar range.
what is very lightly covered LR? I assume that I know, but cannot see how it affects the price, it sounds more like NONlive rock to me, esp at that price. lightly covered sounds more like a coraline reference, which is one thing I do NOT even consider when purchasing LR. LR will become covered in coraline, and depending on the lighting, will probably change color at least slightly b4 it is over anyhow. AS for the other life, either it is LIVE or NOT, no middle of the road there, so lightly covered generally should not affect price all that much, IF you ask me.