The used market for GS500s and Ninja 500s sucks. People keep em til they wreck em, then they buy a 750/1000. If you’re really looking for a good first bike and don’t mind riding around on something older, back in the ’80s all four of the Japanese companies made bikes that are referred to as UJMs. These were bikes that were standard-style bikes (cruiser/sportbike hybrids) with mild, low-maintenance two and four cylinder engines. They’ll make anyone a fine first bike. The Kawasaki ones were the KZ and GPz series. Suzuki had the GS series. Yamaha had the XS/Maxim (shaft drive! woohoo!) and Honda had the CB/Nighthawks(also shaft drive in the 80s). Most of today’s race-edge sportbikes started out being based on these bikes. These bikes emphasized practicality and function over form and were designed as do-it-all generic streetbikes that didn’t really fall into a niche and there are plenty to be had for ridiculously low prices on the used markets. They can be pretty fun too as any owner of a Honda CB550 Four (you heard it right–a 550 cc four cylinder) can attest to.
If you’re not willing to go that old or need something a little more aesthetically modern looking, it’s perfectly understandable. But be prepared to have to do a lot of searching for a good deal on a used bike.