Streamer only

In addition to the budget examples already cited (e.g., RPi, Wiim), there are a bunch of well regarded products that cost between $400 and $1k.  They include the iFi Zen, the Volumio Rivo, Holo Red, Pro-Ject Stream Box S2 Ultra, the Primare Np5, and probably a few others.  I have both an iFi and a Pro-Ject. 

To the OP:  Beware those who try to shame you into spending a lot on a streamer simply because you've got a lot invested in other parts of your system.  The logic only holds if one believes there are material differences in the sound of streamers.  That is itself a somewhat controversial topic, which has been discussed and argued about on this forum and others ad nauseum. 

Let me know if you're interested in educating yourself further on this topic; I would be happy to point you to several other threads where both sides of the issue are explained pretty comprehensively.  As you could probably guess, my own view is that streaming is an area where the greatest amount of misinformation and overspending is occurring these days.  (And for the record, I've been streaming since 2004.)