Looking to purchase a reliable Mercury 20 HP 4-stroke motor? Figuring out the current price scope can help you cash. New Mercury 20 HP 4-strokes usually price between $3,500 and $5,500, depending on features and vendor markups. Pre-owned Mercury 20 HP 4-strokes often fetch for $2,000 to $4,000, depending on condition, usage and overall condition. R