Harvey Norman have the Forza Horizon 5: Premium Edition Electronic Voucher for Xbox/PC for $120 which is ~20% off RRP.
The premium edition includes the following:
*VIP Membership. and
*Two game expansions when they become available.
A good comparison of all the editions is https://www.windowscentral.com/forza-horizon-5-editions#buy
You could also use Game Pass (with any of the discount methods) for the base game and purchase the Forza Horizon 5 Premium Add-Ons Bundle for $62.95 if that is cheaper for you.
Note: It took about 10mins from purchase for the email to come through with the redemption code (the email referred to a link in the content of the email that didn't exist). I went to the Game page on Xbox.com clicked on the 3 dots and selected "Redeem a code", entered the code from the email then selected to install to my Xbox.