@Kampfarsch The lack of world building is due a combination of the manga version condensing the entire first arc (which is just as long as this 2nd one in terms of WN chapters) into 4 chapters, as well as just plain terrible translations by the TL. It not necessarily the Author's fault, and is mostly due to the loss of nuance. Although, I will admit this is pretty generic isekai regardless.
Case in point, I have absolutely no idea where 100 million gold came from, since the manga raws I have don't even mention a price. MC just says "Seydel. Didn't I say that I plan to buy Canaan?" so I assume the TL is just lazy and put random BS down. Later in the WN it mentions her price is 500,000 gold tho.
Another example is the TL not understanding certain Real Life terminologies as demonstrated on page 7, where the MC specifically mentions "This rice looks like Indica Rice. And this oval-shaped one is Japonica Rice!?" which are both very specific breeds of Asian rice. And since the TL didn't research anything some of the world building aspects are lost.
On the topic of rice, the original raws mention [The markets normally don't sell rice in this region, so we don't have it at our shop] implying that it's more of a specialty thing rather than entirely unobtainable. The cat slave even say that they stock "domestically-grown" types of rice (though that's not mentioned in the WN raws)
As for the economy, there's no world building because its literally a carbon copy of japan. 1 gold = 1 yen. The reason why the rice is so expensive is because he bought premium "sushi-grade" rice, which the WN notes is three times more expensive than flour at 6,000 gold compared to 2,000 gold per bag. Keep in mind he bought 10 bags, so 60$ a bag became 600$.
As for how much he started with in the WN, he has 10 gold coins and 10 large silver, which is equal to 1,100,000 gold. As for how he got that, I didn't bother reading through the first arc raws. I just assume he got it from the auction house that sent him to his death, considering that they were selling other Heroes for several tens of millions. Still quite generous if you ask me.