Are you looking for someone who will be an upgrade on Leno, or just a backup who can provide reliable cover? That will make a BIG difference in the kind of options we can suggest.
You probably won't be able to get a really top keeper for that budget e.g Oblak, De Gea, Ter Stegan, Lloris, Neuer, Alisson Becker, Ederson, Courtois.
Thinking about the home-grown quota, perhaps look at Butland or Pickford, should both available for the price and provide decent competition, or maybe Donarumma from Milan. Or just stick with Leno and get someone like Nick Pope on the cheap as a back-up (that's what I did)
I think Cassio from Corinthians is a very good shout. He should be available for less than the budget you have, and is up there with the best goalkeepers in the game in my opinion.