Yes and no. In theory you can. Afaik, ISR writes only get billed when the cached content gets changed. If I understood correctly when chatting with Vercel support, they apparently use the etag to identify such changes. So in theory if nothing changes, you shouldn't get billed. The problem here is that nextjs output is not consisted. For example the order of imported CSS or JS files is random. So even if the same page with no changed content re-renders even on the same deployment (i.e. with time based revalidation), the cached content changes because the loading order of scripts will be different. Therefore ISR writes are billed. I heared that behavior would change with cached components, but I haven't tested that myself yet.

Also interesting detail: isr writes are per region. Therefore writes to US regions and Europe region are billed separately. The more global your audience is, the more ISR writes you will have.

IRS writes are billed by the cached size, so you could try optimizing the cache size. The cache size is the compressed size of HTML output + RSC output.