I was wanting to know if I could use silica sand as base sand in my tank then put a layer of LS on top. I can get this sand really cheep and it is really white and super fine.
I wouldn't do that.
I would suggest you to use search feature of the board. You will find tons of info on silica sand. Type "silica" in the search string.
If you dont want to use all live sand to start, and would like to use the cheaper "dead" sand, see if you have a place neer you that sells southdown. Many people on this board use it, and they just seed it with a little bit of live sand. Saves some money and still looks good as well as not being harmfull to the system. HTH
Sea Goblin