Wow, that's one useful link there! Thanks for the info. Well, if the figures are 2,9 cm tall, that makes them a 1/62 scale (180 body height as reference). This makes sense considering that Hasbro could make vehicles like the Flash Speeder perfectly in scale of 1:60.
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Ah, I just saw the reference on Rebel Scale - they calculated a 1/63 scale for the action fleet figures. That's the scale of most toy cars (HotWheels, Matchbox etc.), but I'd still go for a 1/50 scale model (bus) here. Back in the days I had two buses from SIKU (German) and JOAL (Spanish), which each cost about 40€ new. ebay will be your source to go our a flea market.
You might find cheap seats as loose parts from Asian sellers.