@Veshv
No idea for certain, but I'm guessing that the minimum is 1 bios, since they have been betting it as their "lowest bet to get the shield". This sort of thing happened way back in the Labyrinth game too, coincidentally. The author seems to have an implicit rule of making 1 the minimum bet in his games, probably inspired from poker in order to keep games from stalling.
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I really liked the scene at the end, especially how Kaji called out Baku's name in his time of distress. At first I thought it was completely hopeless (as the author shows 25k bios vs 0 to nail it in), but there may be a way to win still. I suspect Hal or Marco might come into play here, perhaps Hal might lend some bios, or Kaji might get Marco to forcefully steal bios from Floyd's partner or something. If Kaji can get just a bit of bios, he could pull an upset if Floyd thinks he used all his bios up and doesn't bet high anymore. If the winner doesn't get to keep the bet bios (since it wasn't outlined in the wager, just the exilings), then Floyd will have to worry about having bios for his potential upcoming fights against Hal/Marco, so he might not spend too much in the next bets.