How much does the cheapest train from Milan to Monaco (Ventimiglia) cost?
The possible train solutions can be found in the Trenitalia site.
Currently the cheapest train from Milan to Ventimiglia is the regional train. It takes almost five hours and costs 22.25 euros.
It is possible, anyway, to find some good offers for faster trains at a price lower than the one of the regional train. These discounted seats have some limitations, for example you won't be able to change your reservation without paying an extra fee.