@LizzyBee Prices change pretty quickly, even when people aren't stuck at home with nothing better to do than play computer games. But while stock is lower than it was a month ago, I did find some good options in your price range.
These are in order of ascending price, and also in order from slowest to fastest graphics card. All the general information I posted before (
here) is still relevant, and these would all run Sims 3 on ultra graphics settings with some room to spare.
https://www.bestbuy.com/site/cyberpowerpc-gaming-desktop-amd-ryzen-5-3600-8gb-memory-amd-radeon-rx-580-2tb-hdd-240gb-ssd-black/6362427.p?skuId=6362427
https://www.amazon.com/Skytech-Shadow-Gaming-Computer-Desktop/dp/B07WD28Q7R/
https://www.bestbuy.com/site/cyberpowerpc-gamer-xtreme-gaming-desktop-intel-core-i5-10400-8gb-memory-nvidia-geforce-gtx-1660-super-500gb-ssd/6413723.p?skuId=6413723
If you're willing to wait for it to be back in stock, this one would be the best among them, with the strongest processor and the fastest graphics card of the options in the other three models, plus 16 GB memory, which is convenient if not strictly necessary. It also has more storage than most people could ever use.
https://www.bhphotovideo.com/c/product/1558988-REG/cyberpowerpc_gma9020cpg_gamer_master_ryzen_5.html
For monitors, you never did mention what size or resolution you were looking for. To give you some idea though, these are the basic high quality monitors you could get for under $150. They're all IPS panels (the category with the best colors and the widest viewing angles), and they're all the same resolution. And they're in stock or back soon.
https://www.amazon.com/BenQ-proprietary-borderless-Brightness-GW2480/dp/B072XCZSSW/
https://www.amazon.com/Acer-R221Q-bid-21-5-inch-Display/dp/B01DM28XYM/
https://www.amazon.com/Acer-R240HY-bidx-23-8-Inch-Widescreen/dp/B0148NNKTC/
https://www.amazon.com/ASUS-VN248Q-P-1920x1080-DisplayPort-Monitor/dp/B010VG2456/
If you let me know what you're looking for more specifically, I can narrow down the search and do some comparison shopping. Even if you have no idea what you want, it's a good idea to measure the space where the monitor would go and think about how big you want the screen to be.
And of course more questions are always fine.