Can a $750 system sound good?

nice sales pitch...

$750.00 are you joking?

Yes, it can be done ...

I once had a bedroom system that consisted of a Fisher 500 receiver that I bought at a garage sale. A Radio Shack 5-disc CD player. A pair of N. E. A. R. speakers. Stands for the speakers. And hooked up with Radio Shack wire.

Cost for the entire system?

Receiver = $65.00

CD Player = $200.00

Speakers = $400.00 (traded a preamp straight across for the speakers. I paid $200 for the preamp).

Stands = $100.00. They were nice metal stands. I bought them from a friend.

Wire = Nothing. I already had them in storage.

The receiver was in near-mint condition. The sound was really ... really good. If I had to do it over today, I wouldn’t have bought the Radio Shack CD player. While a good player, one can do better today shopping eBay for a good, used higher-end DVD player.

So, I made $200.00 on the speaker trade, so that has to be deducted from the total cost. That brings the overall cost of this little killer bedroom system to $365.00.

Frank

Well, good no but not too bad maybe.
Used original Audiolab integrated - $250.
Some used DVD or CD player - $150.
This leaves $350 for used older speakers and cables.
Yeah, there will be some sound coming out.

Of course!  If you only spend money where it matters. 
Streamer - very marginal gains, if any at all, over a Raspberry Pi 4 plus Allo HAT.  $100. 
DAC - Khadas Tone Board. Excellent. $100. 
Any class D low distortion amp. $300. 
Van Damme cables at $4 per meter. 
Mark Audio Alpair 11MS full range drivers. $150. 
$100 left for some birch ply. 
Then get the free plans for the Frugalhorns Mk3 : https://www.frugal-horn.com

Bingo! 

Another option is to spend $700 on the best active speakers you can find, $50 on an Audioquest JitterBug, and hook them up to your laptop.

That’s a great suggestion. Although not full range could add a cheaper sub later. 

Easily. (Good =/= Great).

Any older NAD Power Envelope, T761 etc, pre-HDMI Denon receiver, locally available tube receiver, occasional bargain Carver etc. $200 - $250

Craigslist floorstanders somebody doesn't want to move. Allison 7, CV D-5, Thiel CS2, vintage Wharfedale, recent Klipsch/Polk. $200 - $500

PS3 for CDs. $50 or less. If there's money left over a Marantz DVD player or any laserdisc player ~$70 - $150.

A little luck, a little knowledge, and a little thrift store shopping and you can do it. 

I can see it. Just don't try to make it resolving, at this price level don't need to expose the warts.

My bedroom system is right around there and is killer.

Just try some High Fidelity Cable NPS-Q45T 3D Enhancer with what ever system you have !  They only sell it at Cable Company or contactenhancer .com  $349

A new shill. Cool!