I picked up a like-new Tamron 17-50mm 2.8 for a bit under $200 I think, so far pretty happy with versatility, creative options, and image quality.
I do also have the 50mm STM and it’s tough to beat for the price.
You didn’t mention which 18-55 kit you had. I believe consensus is the very old 18-55mm non-is was not very sharp. 18-55mm IS is not bad, and I hear the new 18-55mm STM is much improved.