I got an iPod and installed Rockbox, this way I can simply drop music via USB. Batteries are easily replaced for an iPod Classic. The last model is not as easy to open as the others, but its metal case makes it very robust. I will probably keep it for many years.
BudgetAudiophile
A place for AUDIO enthusiast to share, discuss and listen to others people setups
I've had a Fiio X5ii for probably ten years now. Two microSD card slots, plays every format I've tried (MP3, ALAC, FLAC, WAV and probably more), plenty of power for IEMs or larger headphones. Can be used as a USB DAC if you really wanted, also has a line out / digital coax output for connection to external amplifiers and audio systems.
The battery life is starting to falter, so I'll change it out at some stage. The rear cover is held in place with screws, so no big deal.
It shows its age a little with the micro USB port as well, but I wouldn't consider it a deal breaker.
I have also heard that larger cards (like the 400 gig ones) can cause it to slow down a little when scrolling through menus. My cards are 128 gig and I have no problems. Could also depend on the class of card used, it's not something I've needed to consider yet.
Also be aware that the 3rd generation of the X5 is a touchscreen android thing, 2nd gen is similar controls to older iPods, with a similar form factor. They also made other DAPs you could look at (X1 and X3 from memory, there's an X7 as well, but that was touchscreen) but I have no experience with them.
Overall very similar features to the Surfans, but with two card slots and no Bluetooth at all, and I'm pretty certain no USB OTG.
So i had a similar thought as well. I haven't had the time to actually do it but there has been some success with people modding the 5th gen ipods with an SSD and larger battery. All portable players are just so ridiculously over priced. So this seems like it hypothetically could be a really good alternative.
I know this also isn't what you're looking for but there have been some older android phones purpose built with audio in mind and have high quality dacs built in. They would probably also make for a very good cheap portable player.
No good options I have found, but I would love to see the result of this thread. I use both IEMs and Bluetooth headphones depending on the circumstance and the good thing about having both is you aren't stuck with one or the other.
The other question is whether you want things like audio playback speed, chaptering for audiobooks, and marking as read. For someone using this for podcasts or audiobooks those would be useful features, but if it is exclusively music then it won't make a difference.