Don't bother with prebuilts, they're a waste of money. Build your PC by getting parts separately. That said, Sims 4 isn't really a demanding game, if that's the only game you really want to play on your PC getting overpriced video cards or CPU which can handle even the most broken and demanding console ports isn't worth it. You can play the game even using 10 years old GPU just fine, for example.
Can you explain what hardware you have? One thing I can say for sure is that even semi-old (5 years old) i5 CPU is enough for the game, add to that 8 GB of RAM. As for GPU, depends from prices. I'm pretty sure that, say, GTX 770 can easily handle the game, but likely there are better newer cards which are priced the same. Or there is even GTX 660 which should be very cheap to get and can handle the game without any issue as well, from what I saw the game had no low FPS drops on 1920x1080 resolution. As for SSD the only reason to get one is if you want to make loading times short.
