If you want a new device, these are not too expensive and well supported by Rockbox: https://www.rockbox.org/wiki/AIGOErosQK

Or get a used iPod. That's what I did.

Do you carry a smart phone?

If yes, then this:

https://f-droid.org/en/packages/ch.blinkenlights.android.van...

will play flac from your phones local storage (you have to transfer the files to the phone of course).

another ($250) option is https://www.crowdsupply.com/cool-tech-zone/tangara

> Tangara is a portable music player. It outputs high-quality sound through a 3.5 mm headphone jack or Bluetooth, has great battery life, and includes a processor that’s powerful enough to support any audio format you can throw at it. It’s also 100% open hardware running open-source software, which makes it easy to customize, repair, and upgrade

If you are really into good quality audio, I'd recommend a used

  Fiio M11 Plus

It's really good, but even used about 450 bucks. This might be too pricey, so you could then go for a

  Surfans F20

like already recommended (https://www.rockbox.org/wiki/AIGOErosQK). It has no balanced output, but is about 120 bucks and supports Rockbox.

If you more into Android and streaming, you could take a look at the

  Hiby M300

which is also a budget device, but has a pretty modern Android and is a bit more portable than a smartphone.

Maybe it's also worth mentioning Qobuz (https://www.qobuz.com/), the high res music streaming service. Many audiophiles are into this, while I'm not using streaming services at all.

I personally use an old iPod Nano 7g and as backup device my Android phone with Substreamer / DSub and self hosted navidrome. Not hi-res, I don't need this :-)

Warning against Shanling devices. I bought a M0 Pro and it worked fine for about a year and then stone dead. No customer support at all.

Now I'm looking at the Sony Walkman waterproof headband MP3 players. They were released almost 10 years ago, but price, function and quality seem to be good. No FLAC for you though.