Amazon. You can get a full pull up bar set up with dip bars for $100. The dip bars are detachable so you could just have the pull up part if you want. But obviously dips couldn’t hurt. I bought it myself, it’s been great so far
Edit: Estelys Multi-Gym Pull-Up Bar... https://www.amazon.com/dp/B088BMG1W6?ref=ppx_pop_mob_ap_share