I’ve never actually needed primer to paint PLA unless the paint I was using was terrible, and wouldn’t have stuck to the primer very well, either. Tamiya’s acrylics have been entirely issue-free for me, both with a brush, or thinned and airbrushed, and they’re not that expensive, but I’ve also had acceptable results with random fifteen-year-old tubes of really cheap acrylics that were sold more as a children’s toy than a serious paint (although a lot of these tubes had gone bad in that time) and with Humbrol and Revel acrylics and enamels (although their acrylics come in pots that don’t seal very well, so it’s not that uncommon for them to be already cured when you first open them - if you’re buying liquid acrylics for model painting, Tamiya is a better choice).