'Apiece' would be the correct choice here however, I like your 3rd option so... How about, "We have paid 2000 each"? Not always but many times the simplest solution is the best! You want to say, "We have paid 2000 each" so say it! Hope this helps

I think you could also say, "We have each paid 2000". or "Each of us has paid 2000" but I agree with what the first answer said. "We have paid 2000 each" sounds like the best answer.