My advice is to hurry up and wait. If you're going with a gen dial and movement it's worth it to find a good case. There's a lot more additional expense coming when you embark on a build in that rare atmosphere so your budget will be blown again a few more times over.
Like, are you going with a period correct fat font insert? Gen pearl? Top hat crystal or beveled? 702 crown and tube? Just in those 5 parts you can easily spend another $1,800 so yeah, a good case is sorta mandatory.
Unless you get one of our serious modders involved, then they can make a cheap Cartel case look perfect ... for a price. And they have waiting lists.
It's all in the details at this level and the eye has an uncanny knack at picking out something that doesn't feel right. So be patient until the right case comes along, not necessarily the best case. In my last build I waited 3 years for the right dial to come along. It was worth it.