This week in Cheap Seats: Stocks Under $20 segment, we're taking a look at two stocks presenting an interesting buying opportunity: Cassava Sciences Inc (NASDAQ:SAVA) and Vale SA (NYSE:VALE). Cassava Sciences stock is up 2.8% to trade at $19.34 at last check, on track to snap its eight-day losing streak. The equity yesterday hit a familiar floor at the $18 region, which contained a March pullback. So far this year, SAVA shed 13.9%. A short squeeze could generate tailwinds for the shares. Short interest fell ...