Some points I would like to make about publishing economics: This link is fairly instructive as this is Realist Hero 1 on Amazon.jp.
https://www.amazon.co.jp/How-Realist-Hero-Rebuilt-Kingdom/dp/1626929076/ref=sr_1_1?ie=UTF8&qid=1530132036&sr=8-1&keywords=realist+hero
I'd like to point out that the two major bookstores in Japan sell at B&N-style publisher rates without discount most of the time (remember pre-Amazon book buying?). This makes for a more expensive book experience, period.
Because the market is a little more than a third of the prospective US market, anything sold at mass market within a smaller economy turns out to be more expensive as the scale needs to support an author to continue writing.
(Specific as a US market matter): No other country uses agency pricing but the US. As a oversimplification, within the US, unless a contract specifically states otherwise, a vendor who purchases from a source may sell for ANY price that the vendor wants, the source has NO control over the pricing. Amazon actually got into major legal trouble (which they won) with publishers over selling books beneath the source price to Amazon (yes, you heard that right, Amazon was losing money on every sale of a book) because it had something to do with their business strategy.
https://www.nytimes.com/2014/11/14/technology/amazon-hachette-ebook-dispute.html
For equivalent jobs, the Japanese are paid 80% of US rates, so their purchasing power parity is less (meaning everything costs quite a bit more).
This leads to a couple of points:
The floor prices set are NOT just j-novel's prerogative: Let's say for the sake of argument that Sam wants to sell us Volume 1's at $3 in order to entice us to buy more volumes. However, he's having to work with source publishers in Japan that have strict agency models for pricing, and getting a price reduction approved requires source publisher consent. In this regard, that's not going to work as the publishers may consider volume sales to be detrimental to THEIR business model. Sam has some ability to set prices, but there is a clear floor for them. (And having to deal with Japan for academic publishing, I can't get the publishers there to have my translated textbooks sold for less even though I'm the author/editor for McGraw! I'm pretty sure that Bookwalker has the coins system as well to get around the floor pricing problem with agency pricing.)
The Japanese pay more for a lesser product than we do: All those bonuses that we get, the Japanese have to buy multiple volumes for. Also for lesser purchase parity and higher prices as stated above, they get less for more.
Somehow, there has to be a business somewhere: Look, fan translations are "free" to us consumers, but are not free to the content "creators" (and I do mean the translators, web hosting, and ancillary costs) in turns of time and attention. Not to knock on the fan translators, but who outside of the obsessed would want to tackle on some 30 volume monster like Rokujouma? Fandom can get you a couple of volumes, passion can get more, but it's only obsession (which I certainly suspect of the Rokujouma fan turned professional translator) or support that can get the large projects done, because money talks, and it has the best pickup lines.
What I expect from a publisher is transparent and fair pricing. Transparent in that prices are known information to the public, and fair in the sense that I can acquire for that price (this is not true in academic publishing where there are plenty of secret prices and discriminatory pricing models involved). J-novel fulfills the transparent and mostly fulfills the fair (because of the bonuses to Premium members that it's hard to communicate to buyers on other platforms).
As far as price increases, yes, I expect them, but in line with the general business. I do think prices should actually go to the Amazon standard $9.99 sooner than later due to inflation and consistency, but Sam runs the business as he pleases as the owner. I would also support licensing series where the source publisher demands higher prices for the books (Seven Seas) if those books sell here.
Now, look at the Amazon link for Realist Hero. That's the discounted version rather than the usual version in Kinokuniya. That's even a larger ask out of that population than us, but there's enough LN otaku to support that business. I'll do my part, and it's easier here.