Hello from Lindau-Insel 🇩🇪 and welcome to the popular game «Cheapest way to Switzerland». Today: Lindau 🇩🇪 – St.Margrethen 🇨🇭 via Bregenz 🇦🇹.
Place your bets! 🎰🎰🎰

🇩🇪🖥️ DB ticket machine: EUR 24.00 (Bodensee day pass)
🇩🇪📱 DB app: EUR 10.10 (Normalpreis Europa)
🇨🇭📱 SBB app: CHF 8.00 (OTV-VVV combi ticket)
🇦🇹 🖥️ ÖBB ticket machine: EUR 5.80 (VVV single ticket)
🇦🇹📱 ÖBB app: EUR 5.80 (VVV single ticket)

Before you ask: Flixbus to St. Gallen is EUR 7.99, but at least, it's clear where to find the cheapest ticket for it.
Btw: € 24.00 - € 5.80 is € 18.20, which'll get you three to four Meckatzer Weizen. Cheers! 🍺
Disclaimer: Further online research at home just showed that there is a discount on the Bodensee day ticket (the most expensive option) with the Swiss half fare card (EUR 18.00 instead of EUR 24.00). This was not clear for me at the ticket machine.
Anyway, still a difference of more than two Meckatzer.
@dominicstucki Sounds like I need to bring you some soon...
@nordkommission
Wisely, I already had some before I dared to tackle the ticket question... 😅