Under $100: Gigabyte GV-N1030OC-2GI Nvidia GeForce GT 1030 OC 2G Graphics Card
If you're planning to spend less than $100 on a graphics card, don't expect to game with the GeForce GT at 1080p. It adds a boost over Intel's integrated graphics, but many games may simply go from unplayable to a little less unplayable, depending upon how graphically intensive the game is. This does for desktops what Nvidia's MX250 does for laptops. In other words, plenty of games will run on it, but many won't benefit. Cards can come with the chip overclocked, which gives it a little extra oomph as well.
If you've got an old desktop with integrated graphics that don't support the current versions of graphics programming interfaces such as DirectX 12 or Vulkan or if you just want to make Windows feel a little more snappy, a GT 1030-based card can help. The GT line is designed with lower power requirements than the more popular GeForce GTX models, so it can fit in systems with lesser power supplies and compact designs. Unlike most gaming cards, 1030-based cards can be low profile and take up just a single slot, as well as be quieter because they only require a single fan.