The more Bux you sell, the more coins you will make per Bux. Selling 1 Bux will result in 500 coins. Selling 10 Bux will result in 505 coins per Bux. Selling 500 Bux will result in 750 coins per Bux. You can save Bux by purchasing parts on the market individually instead of buying a completed aircraft. Whenever possible, accept jobs that pay in Bux instead of coins.