One option might be to try your nearest university bookshop, especially if you’re living in a major city, because they can usually get the books a fair bit cheaper, even if you’re not a student. For example, here’s UNSW.
Ouch! - you should be able to find better though. As @Belthazar said, try Uni bookshops - lots of second years will be selling their first year texts (ie. Genki I)
I would suggest checking your country’s Amazon vs Amazan.co.jp as the prices tend to be cheaper on the Japanese Amazon page even after paying for shipping. I think the prices fluctuate though so that isnt always the case
I would recommend trying to find a social media group or bulletin board where university students in your area sell their textbooks from the previous year. If you can find someone who used the book you want and no longer needs it, you will pay a lot less than buying it from a bookstore.
Also, if you’re looking at Genki, they just released the third edition (which is what you posted the link to). I haven’t seen it myself, but from what I’ve heard the difference between the second and third editions is basically changes to example sentences, so it might work out better if you look for the second edition instead - it’ll probably have all of the same stuff and be cheaper.
I personally used the second edition when I was starting out and I liked it a lot, but I did use it in a college setting so there’s that. I’m personally a fan of physical textbooks because technology is distracting but to each their own, maybe you’ll find online books work for you.
Keep in mind also that there are lots of free resources that may be as useful as if not more useful than Genki. There are really good video series such as Japanese ammo with Misa or Curedolly that can teach you grammar alongside the free resources like Tae Kim etc
Like other people said also, universities usually carry Genki for much cheaper than retail stores
For Genki, I am even studying with the first edition. Some stuff is outdated like vocabulary for CD player or tapes but I still learnt a ton. My answer key is for the 2nd edition and the exercises seemed to be 90% the same as I did not find any major differences.
I got the textbook and workbook on eBay for € 30 which did not have anything written in it because they came from a former library. So even the first edition is not a bad deal if you are on budget and see it quite cheap on eBay
For me, the cost of physical books is worth it. I have problems reading articles and textbooks in a digital format and it’s a lot less work and time to just have a physical copy.