Well, the taxi at Beijing Airport only allows 4 adults together. You need two taxis which costs about CNY80~100/cab. On the other hand, I think you could book a 7-seat van of airport picking-up, which may charge around CNY300.

Finally, you could take the shuttle bus Line 3 and get off at Dongsishitiaoqiao and then hire two cabs to the hotel. The shuttle bus fare is CNY16/people and the cab fare is about CNY20/cab.