Strange that you say that. The two most expensive dinners for two (other than at charity events etc.) were about 20 years ago, and both in a short space of time.
Considering we are spoilt for choice with Michelin starred chef's locally, we often wonder why we spent that much.
In 'today's money', think Michaels at South Point and multiply x 4.

I can also recall (although I was not paying - KPMG was) having to take Japanese client's to an exclusive London Japanese restaurant just for lunch and it was £200 each without drinks for bugger all. That was almost 30 years ago.