What readily available VR headset can I buy on the used market to walk through a SketchUp Pro home design on an Intel 27" iMac?
Check into HTC Vive headsets - they may work.
I’m not sure what readily available VR software there is you can use with SketchUp on Mac - VR support on Macs is patchy and older macs don’t have the grunt to perform well in VR which is very demanding.
Is there a Gear VR type headset that would work with an iPhone? If the iMac isn’t an option, maybe one of those is.
Just did some double checking
VRSketch Supports Oculus Quest on Mac