If your heart wants a PRX, grab yourself a PRX. But if you've got $1000-ish to spend, I would suggest you take a look at used/vintage watches. That's where you can get some great deals and things start to get more exciting: Longines, Sinn, Doxa, Grand Seiko, vintage Omega. You'll be able to get a watch that may be a "starter" but that you'll still be excited to wear even after you've bought your Santos and Seamaster. Enjoy your search!
I could give you a million suggestions, but I'll keep it to just a few.
If you're open to a vintage piece and you like the PRX look, the obvious choice is an Omega Geneve. These pop up for sale under $1k all the time. Here's one from r/Watchexchange this week: https://www.reddit.com/r/Watchexchange/comments/17bj853/wts_vintage_omega_geneve_automatic_recently/
If you want to buy something shiny and new, I think the Doxa Sub 200 is a phenomenal choice. A genuine dive watch with loads of heritage for $1k new and below $800 used.
Finally, since your two big future purchases are a Santos (traditionally a pilot's watch) and a Seamaster (a dive watch), maybe start your collection with a field watch. A Seiko Alpinist or a Hamilton Khaki Field are both $700-ish new. Then you'll eventually have a really nice land/sea/air collection.