Three 1 phases vs one 3 phase power cost
The bills will normally be the same - unless the 3 phase connection is charged on an industrial tariff while the single phase is a domestic tariff. That's a matter for negotiation with the supplier.

But consider the cost of installing the supplies.

Each single phase supply requires two wires from the substation to your house. That's potentially a total of 6 wires, whereas the 3 phase supply only requires 3 (in Delta).

So in practice those three single phase supplies will be the three phases of a 3-phase supply to save copper. (Normally, with a fourth Neutral to handle any imbalance between them)