An easy way would be to put your sale items on a "Featured Items" page; you could even have a separate "Featured Items" module or page and rename the module "Sale Items" or "Markdowns" or "super deals" or whatever, then in the description field put "Was $100! Marked down!" and put your new price in the item details.
I don't think that there's a way to do $100 $50 in the product setup itself.