Converting Barcode Loyalty Cards to Apple Wallet

So a third-party website has started offering a Web-based tool to generate a "digital" Fly Buys card, seeing as Coles Myer (the company behind the "Fly Buys" loyalty program) don't support Apple Wallet... I am yet to test the card it generated myself, but supposedly it works just as well as the physically card (except that one needs to hold their smartphone under the barcode scanner).

This got me to thinking - most of my loyalty cards have barcodes, so how hard would it be to do a similar thing with all of my loyalty cards in my (Real World) wallet?

What is actually involved in generating a Wallet "card"? Is there a wizard somewhere that will allow me to make my own Wallet "cards" (the one above only does "Fly Buys" cards)? Are there any costs involved (I'd only be using this for my immediate family and I, so I would rather not throw around money like I've just won the lotto!)?