If I ever get the budget, I'll definitely go direct drive. A couple of the European sites look to have the Elite Direto XR for a great price (~$700 shipped and they have the Rizer to go with it for about the same price but aren't shipping that to the US). In the US, the Kickr Core seems to be regarded as probably the top value for what you get.
I don't think a spin bike with speed/cadence will do anything for you. You won't have any sort of way to know if any numbers you make are accurate. If you're just riding for yourself, that may be fine, but you won't be allowed to count in any races and your numbers will just be made up guesses (so you won't even be able to estimate how fast/far you are going). At the very least, get a dumb trainer for which there is a known power curve on Zwift. Your results in races still won't count, but at least you'll be in the ballpark when it comes to seeing how far/fast you are going. If you want to get into power, a dumb trainer and a powermeter (used powertap wheels, used Garmin V3, or Assioma Uno among many other choices) could get you riding in the $5-800 range, but then you're almost at the price of a direct drive smart trainer, so it depends on if you would want the power data while riding outdoors in the future as well.