I've been making adopts on the site for nearly a decade, too. I used to sell one adopt for 50kt, which I now sell for 800g each (base) and customers are still going strong. I'm very glad that people are starting to charge more for their adopts.

I think site inflation has a lot to do with it, but also the popularity of skins. I think 400g - 500g for an adopt being a similar price to a 500g accent is a pretty fair equivalent.