Rudyball

The outer lenses are burnt bad enough that it inhibits night driving - 2011 RX 350 - HID Headlight ***'y options are totally expensive - can I replace them with the cheaper halogen ***'y option?

Clutchless

No because the wiring is different as are the component parts, and it will be much more expensive in the long run to try and do a conversion than just replacing the lenses. Also you would probably end up with a permanent warning light on the dash afterwards.
I would first look into getting them restored by an auto detail shop or other place that restores headlight lenses. Many times that is all you need.
There are also used ones on eBay or other online used parts sites.