Given what you'll be paying, you'll likely be renting an apt and not a corporate rental (assumption on my part, as that wont' get you a corp. furnished apt). You should probably just make appointments with various property managers directly. I used
Apartments for Rent and Resources for Finding Apartment Rentals Nationwide - ForRent.com when I was initially looking- the zip code for the Plaza area is 64112.
Some of the nicer places, around or on the Plaza: Churchill, Sunset Tower, Sugrave/Regency (might be over your range tho), Montreaux on the Plaza.
Dunleith, Plaza Terrace, and Plaza Apt Center are awful imo.
There are a lot of rentals around the Plaza and many manage multiple buildings. Good luck with your hunt!