@simmerdown18 I'm sorry for the late reply. I've been searching every custom build site I can find, and none of them quite had what it sounds like you're looking for. The issue is, the mid-range graphics cards are so scarce right now that all the custom build sites, and even many stores that sell pre-built models, have significantly raised the prices. As an example, an Nvidia 2060 is usually around $80 more than a 1660 ti or Super, but models with a 2060 are more like $200 more right now, and upgrading from a 1660 Super to a 2060 also costs around $200. Faster cards are proportionally more expensive than they should be as well, since everything is sold out and people are desperate.
You still have options, of course, especially with potentially $1,500 minus the monitor cost to spend. The question though is how much the available upgrades are worth to you. There are essentially two paths you could go. One is to get high-quality components in a custom-built PC and pay about $300 more than you would for a prebuilt system with the same hardware. The advantage of course is that you'd pick exactly the components you wanted.
The other path is to get a custom build from a company (Dell in this case has the best prices) that uses lower-end components. The motherboard, power supply, etc. would be perfectly fine for your current needs but might not support the upgrades you might want in a few years. Consider these two configurations, both with a 2060 Super; the differences are the stronger processor and extra RAM in the second:
https://www.dell.com/en-us/shop/desktop-computers/dell-g5-gaming-desktop/spd/g-series-5000-desktop/gd5090g520s?configurationid=a2c36dc9-bb78-41f9-bc40-108a1ef6cd03
https://www.dell.com/en-us/shop/desktop-computers/dell-g5-gaming-desktop/spd/g-series-5000-desktop/gd5090g530s?configurationid=334d4580-f7ea-4e38-8404-33ab1e078e04
(If you liked the first but wanted 16 GB RAM, you'd be better off buying it separately: you could get another 8 GB for around $35 rather than paying Dell $100 extra.) A custom build with a 2060 Super from a company that supplies high quality components would be around $1,450. Prebuilt options with a 2060 regular (not Super) are still $1,100 and up.
A 1660 Super would still be more than fine for Sims 4, and significantly cheaper, although still in the $1,200 range. Prebuilt PCs on the other hand are under $1,000. And Sims 4 doesn't need and wouldn't use more graphics power than that, even with a giant pile custom content, on a standard 60 Hz 1080p monitor. I know it's not the firepower you're imagining, but it would be perfectly fine for now and in all likelihood for the entire run of Sims 4. By the time you wanted a new card, the market should be normalized again.
As an example of reasonably high quality components, these two builds both include a 1660 Super and are under $900.:
https://www.amazon.com/CyberpowerPC-Xtreme-i5-10400F-GeForce-GXiVR8060A10/dp/B08FBK2DK5
https://www.cyberpowerpc.com/system/Gaming-Instant-Ship-GM-9910
The main difference is the processor, although the option from Amazon doesn't go into as much detail about the components. The one directly from CyberpowerPC has a good motherboard and power supply, not the ones I'd choose if I were customizing a build but certainly good enough to support upgrading the processor or graphics card in the future. As for the Amazon one, Cyberpower doesn't use low-quality components at all; you'd be getting surplus parts from its custom-build stock.
If none of these are what you're looking for, let me know why, and I'll go back and try to find something closer to what you want. (It won't take me nearly this long this time around.) However, the options are limited right now, so you'll probably need to compromise somewhere along the line.
As for monitors, it's easy to find good options, and there was plenty of stock when I looked a week ago. Just let me know what size screen you want and whether you'd prefer a higher resolution.