Actually you are wrong. It can be used on it's own without being piggy-backed onto another head unit. The heading on the HDA-5460 webpage is "In-Dash Add-On/Stand Alone HDD (Hard Disc Drive) Player"
The head unit it is pictured with is not "another $1100.00" either. The MSRP listed on the site for the CDA-9815 is $500.00 USD. I actually bought it for less at $600.00 CDN. It's all right there on the website in black and white boss...