Which do you need, a cordless drill or impact driver? Of course you need both, at least I do. If you've never tried an impact driver take the time to do so, and time to stand in the checkout line once you decide to buy it.
Impact drivers pack a powerful punch but often leave behind a trail of stripped screws and split boards. The 18V LXDT06Z Quick-Shift Mode 3-Speed Impact Driver by Makita automatically reduces impact force and rotation speed in the final seconds of driving for a level of control you'd otherwise look for in a less powerful drill/driver. About $180 from makitausa.com | thisoldhouse.com