Upgrade DAC for an Oppo BDP103

Greeting friends. I recently acquired an Oppo BDP103 as an all in one solution for my audio/video needs. My primary use is for audio playback of cds and a few SACDs plus the occasional movie. I've been toying with the idea of adding a stand alone dac to improve the 2 channel audio reproduction. I've not dipped my toes into the water in this area before so I'm curious, how far up the dac food chain do I have to go to realize an audible sound improvement? In a dollar a cents basis, $400.00, $500.00 ? Used of course would be a strong consideration. Any recommendations for a reasonably priced dac that is not a lateral change? I appreciate inputs and commentary.
My Schiit Modi Multi connected with Blue Jeans digital cable made my 103 sound more musical, less clinical (better to my ears), but will only play CDs, not SACDs or other formats. 
I believe used Bryston BDA-1 currently going for around $700.
This is a very good DAC which I have personal experience with.

Brand new Schitt Bifrost also goes for around $700.

Brand new Chord Qutest goes for around $1600.
This is an excellent DAC that I can highly recommend, and currently have one in my main rig.

Used Ayre Codex would be another good choice. I’ve seen them going for between $950 and $1100.

Given you got the pocketbook, I’d be aiming for the Qutest or the Codex.

This may or may not be important to you.
The Bifrost and the BDA-1 are PCM only.
The Codex and the Qutest both support DSD.
Getting an external DAC is surely the way to go.  You will get many suggestions.  Do your research on this board and elsewhere.  You're not restricted to this thread.

If you like your SACDs, know that you will not be able to play them through your new DAC--even those that do permit the DSD format--unless you rip them.  Fortunately the Oppo 103 will let you do that.  They will sound great.
Yes... A good external  DAC can make digital sound more musically involving.. schiit audio has some great choices for little money considering the type of DAC you’re getting..