@Virginia594 I think other than a sink, everything else can be added very easily. You can get a portable kitchen island at IKEA or Wayfair, hotplate, mini fridge, a handful of very basic cookware items and a microwave. I think it should be permanently there. You should be able to do this under $200. As long as you have clear pictures and description, no one will expect more. I personally think kitchen/kitchenette is a huge part of what attracts people to Airbnb so I would say it is worth it. If the bathroom is very close, there is no need for the sink installation, you just need to make a desicion on where and how dishes are washed so food waist is not being dumped in your sink.
Having said that, you have amazing reviews already so maybe don't fix it if it aint broken?