Yen Press has been doing a simulpub of the chapters as ebooks. IE: They not only are releasing the physical and ebook editions of the manga volumes, but on the 25th of every month when Big Gangan magazine goes on sale, they also publish an ebook of the new chapter as well for $1.99. Since this is a monthly series, that puts your total cost if you buy each separate chapter around $8-10. Not sure if they put 4 or 5 chapters per volume. Kusuriya no Hitorigoto serialized in the same magazine was 4 chapters for Vol 1, for comparison.
For example, Ch 17:
https://www.amazon.com/Goblin-Slayer-Chapter-manga-Serial-ebook/dp/B076H1GYKY/
Disclaimer: I thought this was a progressive idea of them to do and wanted to raise awareness, no shekels were harmed/earned during the shilling of this series.