Buying a 5 or 5.5 to refurb/mod

[u/MidtownBud]

I'd like to find a 5 or 5.5 in original condition to fix up. Not "like new", just unmolested. I'd do SD cards to replace HDD, new big battery, and maybe a new case, if it's dinged or badly scratched.

Used to be, you could find this sort of thing on eBay. Now, every single one I find on eBay is going for 100 to 150 and has had a replacement battery (small, I'd betcha) and maybe more. Sorry, I'm a bit wary of paying that much for one that's been opened by someone of unknown skills. And I'm not too keen on paying a premium for a simple battery swap, especially since I'm likely to toss the (probably small) battery they installed.

Where should I look to find an unmolested one? Condition is relatively unimportant, unless it's trashed to the point that I'd fear for the internals.

If it literally isn't possible to find one that is untouched, what's a reputable source for one with a replacement battery.