Hi
lernauta. To err on the side of caution, I'd recommend that you not going any lower than the AMD Radeon RX 6600 ($200 or less). And I would discourage you from buying the RX 6400 or 6500 XT for a few reasons...
They are both PCIe 4.0 x4 (4 lanes) 64 bit (memory bus) cards. Also both the 6400 and 6500 XT only have 4GB of VRAM, which may be limiting for holding textures, even at only 720p. Since your CPU is only a Ryzen 5 4500, I assume that you motherboard has a PCIe 3.0 x16 slot. Also, even though your RX 6600 may be "overkill", I'm aware that your R5 4500 only has 8MB of L3 cache, as opposed to the 32MB of L3 on a Ryzen 5 5600, which may be limiting to your framerate. In addition, you mentioned that you have 16GB of system RAM, but we don't know if it's in single or dual channel configuration, or what speed it's binned for, or set to in the BIOS.
TLOU Part 1: If you were attempting to play at 720p @ max settings, then I suspect the RX 6600 would simply be adequate for this goal with your rig.
RE4: Perhaps this would achieve 720 @ 120 FPS or 1080 @ 60 FPS (max settings) with a RX 6600.
Both estimates above are wild assumptions based on the two YouTube videos below, and figuring that 720p is approximately half the amount of pixels (921,600) of 1080p (2,073,600). You should watch the videos yourself and come to your own conclusions about achievable framerates.
Addendum: Despite my opinion, I would have to agree with
35below0: A RX 6400 new for $50 is practically free. I know of nowhere in the US that you can purchase a new RX 6400 for less than $120 USD. If you can truly find it for $50 then perhaps that's worth trying that first. But otherwise, I think that an 8GB 128 bit GPU, such as the RX 6600, would be a longer term investment. Just make sure to buy from a retailer that has a no-hassle return policy, in case I'm wrong and it turns out to be massive overkill. Best of luck and happy gaming.
2nd Addendum: I also like
punkncat's suggestion: If you can find a RX 580 8GB (not 4GB) GPU used for $50-$60, then I'd like that for you too; even more than the RX 6400 for $50. But I think the RX 580 8GB might only be able to maintain 720p 60 FPS at low settings in TLOU Part 1. Long term, I still think you'll be happier with the RX 6600, if you can swing it's $200 USD price tag.
** notes **
View: https://www.youtube.com/watch?v=JA_oAqLJ9bA
View: https://www.youtube.com/watch?v=pw6xXUkXi6M
https://www.techpowerup.com/gpu-specs/radeon-rx-6600.c3696
AMD Navi 24, 2815 MHz, 1024 Cores, 64 TMUs, 32 ROPs, 4096 MB GDDR6, 2248 MHz, 64 bit
www.techpowerup.com
https://www.techpowerup.com/gpu-specs/radeon-rx-6400.c3813