I see translators who offer discounts as soon as the total tally of a project exceeds 15,000 or 20,000 words. I’ve never seen the logic for this discount, and I will try to explain why.
Supposing you translate 3,000 words daily, it will take you 15 days to complete 45,000 words. Unless half of the text is repeated, and your client or the agency will deal with it.
Our productivity does not increase after translating 3,000 words. It follows the same rhythm because languages are a living being and context means the world. So even if you work with translation memories, you’ll still have to check every comma to see that what you have written makes sense. And you still have to type your 3,000 words.
Personally, I prefer short projects that do not tie me down more than 2 or 3 days. Why? They are so short they make me stay concentrated. Above all, I usually learn a lot. And to top it all: I never have enough time to get bored of them.