My $35 bidet is awesome and just diverts water from the tank. It took less than 10 minutes to install: remove seat, place bidet, replace seat, unscrew tank water supply, screw in water splitting hose. You don’t even need to turn off the water, that’s how easy it is. It’s great for renters, too, because you’re not actually making any modifications, and it’s easy to remove with no trace.

Mine’s a Luxe, but there are several like it in the same price range.