Hmm, yeah, that is an old monitor, and a sort of oddball resolution of 1440x900, giving a 16:10 aspect ratio. Most monitors are 16:9 (widescreen, same aspect ratio most TVs use these days), and some are 21:9 (ultra-wide).
The overwhelming majority of monitors in use are 1920x1080 resolution, which is a 16:9 aspect ratio.
For the time being, if his monitor still works, it'll be fine, though I imagine, depending on his age, he'll want to upgrade at some point.
I'd actually save a little and go with the 4GB RX 570, and one is available (after $10 instant discount, and $20 mail-in-rebate) for $99.99
https://pcpartpicker.com/product/tF648d/xfx-radeon-rx-570-4gb-rs-xxx-video-card-rx-570p427d6
Are you by any chance located within a reasonable driving distance close to a MicroCenter? If so, they have some great in-store deals.
In-store, you can get the Ryzen 5 1600 for $79.99, and get the ASRock B450M Pro4 MicroATX board for $79.99. Buy them both together in-store and they knock another $20 off.
For the rest of the parts, here's what I've got:
PCPartPicker Part List
Memory: Corsair Vengeance LPX 16 GB (2 x 8 GB) DDR4-3000 Memory ($57.99 @ Newegg)
Storage: Crucial MX500 1 TB 2.5" Solid State Drive ($99.99 @ Adorama)
Video Card: XFX Radeon RX 570 4 GB RS XXX Video Card ($99.99 @ Newegg)
Case: Thermaltake Versa N21 ATX Mid Tower Case ($44.99 @ Newegg)
Power Supply: Corsair CX (2017) 550 W 80+ Bronze Certified ATX Power Supply ($69.98 @ Amazon)
Total: $372.94
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2019-12-09 22:58 EST-0500
This memory kit is on Corsair's compatibility list for that motherboard. I stuck with
@keith12's case suggestion as I am utterly hopeless when searching for cases.
Unfortunately, even assuming you're conveniently close to a MicroCenter, the CPU and Motherboard still add $160 to that, so $532.94 AFTER rebates, and BEFORE tax.
Am I correct in assuming there's a keyboard and mouse from a previous system? (edit: ah, yes, you mentioned keyboard and mouse earlier, I missed your reply to my previous question on that) Are there any other parts being carried over, say, hard drives or SSDs?
Am I wrong in assuming there's a previous system involved at all?
To save a bit more, you might need to go with a smaller SSD, or no SSD, and resort to a regular HDD. That would shave about $40 or so off. That might JUST cut it under the wire of $500 after rebates and before tax.