Machines inside Terminal 1 and 2 deliver the airport product — the €10 round-trip 'Aéro' card — and, per the operator's fare grid as reported by actu.fr at the tariff change, not the €1.70 singles or day passes sold everywhere else. A first-time visitor with no card pays €10 plus a €2 refundable card deposit to go one way into town.
Line B shares the airport tracks and turns south to the CADAM administrative centre instead of the centre; from the other side, alternating airport services end at CADAM rather than Port Lympia. And the airport's own pages state both tram lines and bus 12+ skip 1 May completely.
Bus 12+ explicitly sells nothing on board ('Pas de vente à bord'); fare evaders on trams and buses ride into a fine. On the intercity ZOU coaches the airport page warns of a +€0.40 surcharge for buying on board — the €21.40 Open Payment fare versus €21.80 from the driver on line 80 shows exactly that gap.
The flat Monaco fare is legal and fixed at €95 (€85 Cannes, €72 Juan-les-Pins), but the express 80 does airport → Place d'Armes in about 50 minutes for €21.40 with your bag in the hold. Groups split a taxi, singles burn three times the fare.