I own a pixel 3a phone but I wish to up my audio game by using flac files. Problem with the pixel is that it doesn't have an external storage slot.

I don't want to buy a DAP because I like the idea of perhaps using a custom ROM or being able to switch audio apps etc. So I want to use a separate phone just for audio.

Here's what I want: - Phone should be able to play flacs to a very high quality/standard - Should have an external memory slot that can be expanded up to 512GB or more. - Must cost around £50-80 - Bonus if a custom ROM can be used which still preserves the audio quality and features

Is there anything out there that can fit my requirements?

I've read about the LG V20 but I don't think it was sold in the UK and the prices on eBay are in the 100s.

Are old Motorola G series any good for audio?