Lenses are expensive: things like autofocus, modern coatings, and even just the fact that you're buying something new all contribute to the price. When it comes to saving money, vintage lenses are often a fantastic option, generally coming with unique looks that are difficult if not impossible to recreate in post.
While the images you get out of a vintage lens aren't as sharp as a more modern equivalent, they more than make up for that in character. Not every lens has to be so sharp you can cut yourself on it; there is something to be said about something a little softer and dreamier with a defined look being prioritized over absolute sharpness. Heck, Leica sells a Soft Focus lens, the Thambar-M 90mm f/2, for almost $6,500.
In this video by Tony Northrup, he explores the advantages and disadvantages of Vintage Lenses on the Fuji X-T3. He uses a Nikon-Fuji Focal reducer to keep a near-full frame FOV and compress the image onto the APS-C sensor of the lens. Personally, I would recommend a Canon to Fuji adapter, as this way, you can adapt more lenses (M42, Pentax K, and even Nikon G can all be adapted to Canon with infinity focus, allowing you to widen your options considerably)
Tony brings up some great points about using vintage lenses on mirrorless bodies, specifically regarding things like focus peaking, being able to look through the viewfinder in black and white, as well as the ability to have real-time aperture priority. While I don't agree with when Tony says that the lenses are only really good for snapshots (I spent the first few years on exclusively manual glass and got some fantastic and sharp-enough images that I've printed out rather large), he does a good job of outlining how to get started with vintage lenses.
On modern lenses, we generally deal with what is called "focus by wire," where turning the focusing ring tells the camera to move the autofocus motor in relation to how quickly or slowly you move the focus ring. On vintage lenses, the focus ring turns a physical helicoid in the lens and moves the elements the same way every single time.
Have you ever shot with vintage lenses? Why or why not? I should give you a warning: with how cheap some of these lenses are, you will find yourself collecting them and hoarding them.