It truly depends on the series. I can only read one book at a time (my brain just can’t keep track of the plots if I’m reading more than one, it’s painful) so that makes things slower but if it’s a series I’m really loving, I’ll binge the entire thing in a few days. Some other series will be interesting at first but then grow more and more tedious for one reason or another. My latest series I read (Three Dark Crowns reread), I completed in a week. I highly recommend. ☺️
I’m in the States but I tend to hit up a lot of local libraries as they tend to have sales to get rid of older books/books that aren’t getting as much traction.