This is more of a political/marketing question than a technical one.
Therefore, the only way to know is to ask the electic utility. They
probably bill you per kWh, which means it doesn't matter.
where it is located and the system voltage. If you want a 30 kW supply
for an apartment building in a city, a three phase 220/380V service is
cheaper than a 220V single phase service.
If you instead is located in a village and need a 3 kW supply for a
home, a single phase 220V will be cheaper. If you want you can find in
depth analysis of cost/benefit for different distribution system on the
net.
One of the reasons is the load balancing: It is difficult to balance a
3 kW three phase service: Each phase will carry only 1000 W. Typical
single phase loads like a hairdryer or vaccum cleaner draw more than
this and can't be used despite the fact that the supply is 3 kW.
For this reason, you will rarely find 3-phase supplies smaller than 10
kW.
On the other hand, 220V single phase is an inefficient way to transfer
a lot of power. At 30 kW, you can load every phase with 10 kW. There
are almost no single phase loads this large and the balancing therefore
is little problem.
Three phase requires less copper than single phase to conduct the same
amount of electricity. As copper is expensive you will rarely find
single phase supplies larger than 30 kW in countries with 220/380V
systems. (It is a different story in North America)
With 3-phase you can also run large motors. Large single phase motors
are very expensive.
