8BitDo is now selling a Bluetooth receiver for the Sega Saturn for $25. They're claiming "Virtually Lag Free", but as usual they don't post any actual measurements. If you're willing to spend an extra $10, you can get one based off of BlueRetro that's been measured with low-latency BT controllers
I’m tempted to get this to use with their BT Genesis controller I have, but I was having connection problems with their GameCube BT adapter losing connection intermittently so I’m not so sure about this one.