This seems like a completely artificial problem. He can build his house for 4000 gold coins, which would be a lot for the average inhabitant of this world... But it's not at all for him, right? His harem hunts those death hawks daily, which sell for 1.5k a pop. He sold the dragon for 10k and that cyclops for 50k. So the cost of building that house is like insignificant compared to his average income. Yeah, that shrine store is a expensive comparatively, but he can just slightly decrease the amount he buys from it for one day and the problem would be solved. The house is a one-time purchase anyhow. And yeah, uh, if he'd just look into producing those goods himself instead of sinking fucktons of money into the shrine store, he'd be the richest person in the isekai in no time. Given what this manga is like, the author certainly doesn't seem like the sharpest tool in the shed, and the depiction of economics is reflective of that.