While it doesn't pack as much software features or premium hardware as the Samsung Galaxy Note 8, the $130 LG Stylo 3 offers an embedded stylus at a fraction of the cost. It's available for Boost Mobile and Cricket Wireless users.
If you want a built-in stylus for cheap, the LG Stylo 3 is your only choice. Another other option is the Motorola Moto E4. It doesn't have a stylus, but it also costs $130, is splash resistant and its front-facing camera has its own flash.