You could just get a reverse-ring to mount one of your existing lenses backwards, but I want to steer you into the rabbithole of vintage lenses anyway
Ebay has loads of all kinds of them, and many are in no way behind modern lenses in terms of image quality, while being super affordable.
But then there’s also lenses people specifically seek out because they aren’t perfect, and exhibit visual quirks that make them interesting for creative work.
The soviet Helios 44-2 for example has some strong spherical abberations going on, producing what most people call a „swirly bokeh“.
This lens has been used in some scenes of The Batman, and they even modified their expensive anamorphic cinema lenses to look more like the Helios.