At the risk of having hundreds of HR forum members descent on me for heresy....
If you're not mixing, don't worry about studio grade monitors. Spend the money that would have gone on speakers on acoustic treatment for your "voice booth". Do a bunch of trial recording and play them back on everything from your best stereo to the car CD to your iPod and, when you're happy with the sound, lock in the mic position and acoustic treatment of the area.
Buy decent headphones to wear but don't go silly on them either until the money is flowing in.
Once you start mixing fully producedand mixed ads or idents, THEN you need to invest in good monitors.
Good luck!