If they cost as much as a used car, you can always use the excuse I made up when I bought my last pair ($600 for frames and because my prescription is most definitely not boring, I'm pretty much looking at a grand to start, regardless): I'll be wearing these every day for at least four years, so that's ($1400/(365*4))=significantly less than the cost of a cup of coffee/day.

And if you love them, you might even be able to just get replacement lenses next time you need a changeover, which amortises the cost of the frames over an even longer period of time. I got almost nine years out of a beloved set of frames that way, so they ended up costing almost nothing! Or so I told myself.