Your search for "AIR-CT3504" revealed the following:
Cisco AIR-CT3504-K9 4x 1GB RJ45 Wireless LAN Controller for up to 150 AP's
SKU: NSH-6760
Condition: Seller refurbished
Shipping: Overnight Options
Warranty: 365 days
$ 203.99
• Only 2 remaining
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Cisco AIR-CT3504-RMNT 3504 Wireless Controller Series Rack Mount Tray
SKU: NSH-7741
Condition: Seller refurbished
Shipping: Overnight Options
Warranty: 365 days