Quite a few. They were all the rage when I got a Cowon iAudio G3 for Christmas in 2005 that held a whopping 512 MiB. Ran for like 25+ hours on a single AA cell. Part of why I can't take modern-day players lasting 8 hours on a 2000+ mAh lithium cell overly seriously, let alone their absurd price tags. I'd be paying around 200€ for a nice single function device, but definitely not 1000. You can only get away with that in a multifunction device that's good at several things, like a modern phone.
This is why I wish someone would bring out a well-performing and well-designed player explicitly with a Rockbox-based firmware in mind. RB would still take a substantial amount of work to bring it up to a modern standard (*cough* BT stack *cough* exFAT *cough*), but it would be massively better than starting from scratch. It's got gapless playback, RG support, Meier crossfeed, parametric EQ and many other features already.
I actually thought about starting an open-source hardware project for such a project on the EEVBlog forum about 2 years ago, complete with long-term sustainability in mind (e.g. choice of battery - some sort of common user-replaceable type - or being somewhat easy to repair if need be, automotive grade ceramic capacitors, conformal coating etc.). It's not like the demands on such a device are changing on a daily basis, so you might as well get it right once and be done with it. A couple of physical buttons, a decent display, enough oomph for common audio formats (but I mean even an iPod 6G had that), SD card slot(s), etc.. I'd be quite happy with the capabilities of my Clip+ if it wasn't such a tiny thing with tiny buttons (not ideal for my Euro-Paws(R), and using the on-screen keyboard is a chore at best) and a tiny display that won't fit much of anything at a size I can read, with an aging tiny 200 mAh battery.