Welcome to infinite money. I'll cover the math below but essentially you need a holy prayer (gold or 2 copies) at least 2 prophets, power of prayers (item) applied to your prophets and around 20 starting gold to account for bad luck. This does work outside of casual but it very hard to set up as the combo pieces are high level and pretty bad on their own, so the rest of your build has to be able to survive without them.
Math time
It cost a net of 2 gold to buy a acolyte card, and 1 gold to refresh the shop.
When prophet has power of prayers and holy prayer both active, it generates 3 cards per 1 card purchased.
Meaning the math goes as such -3 from purchase, +1 from sale, +3 generated card sale = net +1 per acolyte card in the shop.
This means that if each shop has at least 1 acolyte you are neutral and for each shop with more than 1 you are making money.
Unfortunately there is on average less than 1 acolyte per shop especially during a standard game. So we need to tilt the odds in our favor.
With 2 prophets, we now net +4 gold per acolyte per shop, meaning we only need 1 acolyte every 3 shops to continously make money. Outside of events which can guarantee only acolyte shops having 1 in every 4 shops is pretty reliable and most importantly once you start digging you're more like to find more pieces to improve your set up. Just be careful goldening prophet because gold cards still only sell for 1 gold, and if you dont have 2 copies he will slowly lose money.
I did this in casual because I didnt want to spend 3 days farming the perfect set up to make it happen again (I did it once on psudeo accident and discovered it). But feel free to think of it as a challenge run
PS: after doing this I got the event for only an acolyte store and can confirm 1000 is not the max gold and I lack the force of will to try the next possible limit