That's really strange. I don't think I've had more than 2 cities bribed, total, in all the various campaigns I've played. I can't say why you'd be getting it constantly.

However, I have noticed the "Pull unlimited money out of my ass" thing several times. I played a Gaul campaign once, where the Julii were in a similar position, with just Arretium, Ariminum and Segesta, yet managed to put together 2 full 20 unit armies and still amass over 70K denarii in the treasury, at least according to the financial rankings. It makes me wonder if the AI pays maintenance. In my current campaign, as the Julii, I own a large part of the Aegean (Athens, Corinth, Sparta, Kydonia, Rhodes, Halicarnassus, Sardis and Pergamum), Salona, Segestica, Iuvavum, Tara and all of Gaul. The Bruti have managed to take Apollonia, Larissa, Thessalonica, Byzantium and the other Thracian city (the name escapes me now), and Campus Gepidae. Yet, for all the small size of what they own, they still have the largest army in the world. I'm supporting a 20 unit field army + reserve units in Asia Minor, a 20 unit army near Numantia, 3 full 20 unit armies in Germania on campaign, plus reserve units and garrisons, and they've got a higher ranking military than I do. I have no clue how they can keep building.