I've never seen an option to pay for one specific article. I think I'd be more inclined to do that than to subscribe. The guardian offers the ability to donate but if I recall it was only in amounts that around $10 or more which feels like it would cover several articles. You could just donate that much and personally consider it a down payment on however many articles you think that buys, but psychologically a cheap price to buy the one specific thing you're trying to read feels more reasonable when you're making the decision to pay or not.

Another idea I've heard is basically getting a subscription to access a big basket of publications with each publication getting paid out of a central pot based on what someone chose to read. I think the various publishers hated this idea from what I heard so it was something of a non starter.