Looking to get a trustworthy Mercury 20 HP 4-stroke engine? Understanding the present price range can save you funds. New Mercury 20 HP 4-strokes generally cost between $3,500 and $5,500, based Yamaha 350 outboard price on accessories and dealer fees. Used Mercury 20 HP 4-strokes often go for $2,000 to $4,000, affected by state, hours and complete