Can anyone recommend a wireless flash set up for Sony A200 camera/Sony F58-AM flash unit?
You'd use the pop-up as a trigger; it will provide TTL control of the F58-AM. The only thing you're missing, really, is the off-camera shoe (to mount it on a lightstand) and that's the same unit as the Minolta/KonicaMinolta OC-1, so you may be able to pick one up fairly cheaply on the used market. If you don't want the on-camera flash to influence the lighting, you can put a bit of card in front of it (it doesn't have to be white card) -- as long as even a little bit of light leaks from the pop-up, it should be enough to control the remote flash.
Your other option is a radio trigger like the Cactus v4 trigger with a hot shoe adapter to provide the interface. I don't know anything about the adapter, there may be others around as well, but the Cactus triggers are okay, not great, but okay, and generally work in a reasonable range for home studio fun (I have them and have used them on studio strobes).
Pixel and Phottix radio flash triggers have Sony/Minolta hotshoe versions, but you can just use hotshoe adapters with any manual radio triggers, since TTL communication doesn't matter. If you need TTL over radio the Pixel Kings and Phottix Odins both have Sony/Minolta hotshoe versions (but they obviously don't support the newer Sony iso-compliant hotshoe flash gear).