RegentGames via Eneba has $50 Xbox Gift Card (Instant e-Delivery) which can be bought for $40 with a discount code from Eneba.
Follow the instructions below to get the indicated prices:
Service fees apply. Use the indicated discount codes to reach the following prices (after coupon and service fees).
Instructions:
1. Select your offer and click "Buy Now"
2. Go to cart
3. Select payment method PayPal or Credit Card (Service fees will be applied here)
4. Apply discount code XBOXTHREEFIDDY
5. Proceed to checkout with an end-price of $40
*Price is subject to change by a few cents due to currency exchange rate volatility