When I ordered my Dot I also ordered
these speakers for $34.99 USD (they have gone up since then). The speakers arrived well before the dot, but when the Dot finally got here I was ready. I installed the Dot, and tried her without the speakers. She worked fine, and was loud enough to use in a quiet room. but not really good for music. Then I plugged in the speakers with the built in 25 watt amp set to about three quarters volume (full volume resulted is serious distortion), and to my non-audiophile ear was every bit as good as a stand alone Echo, with the added benefit of full stereo.
Not being an audiophile, to me the difference between $100 speakers and $1000 speakers is $900 wasted, for those more discriminating the extra money may be worth it.
If I had it to do over, or again, I'd use BlueTooth speakers because from reading another post it appears that with BlueTooth if you turn off the speakers, Alexa automatically switches to her internal speaker, but with wired speakers she does not. You have to physically unplug the speakers to get her to use her own. Maybe I can find a BlueTooth dongle that would work.