Forza Horizon 3 Standard Edition for £38.97 from the Singapore store.
1) Purchase the $20 & $50 gift codes from the Singapore Microsoft Store.
$20 = https://www.microsoftstore.com/store/mssg/en_SG/pdp/SG-$20-Xbox-Digital-Gift-Card/productID.299585900
$50 = https://www.microsoftstore.com/store/mssg/en_SG/pdp/SG-$50-Xbox-Digital-Gift-Card/productID.299586000
2) PayPal is a checkout option and you can use the following billing address if required:
7 Raffles Boulevard
Once payment has gone through you'll receive the codes instantly.
3) Redeem the gift codes on your account and purchase the game using your newly acquired credit.