Connections within Finland
From Helsinki there are several options for traveling to Savonlinna (Savonranta). The cheapest way is with the Omnibus, which can be booked from € 8, if you do that a little longer in advance. (Pets are not allowed)
When you arrive in Savonlinna and you do not have your own transport? Then I can pick you up for fuel costs (about € 15).
Rent a car
If you do not come with your own car, you can rent a car in several places. There are several car rental companies. SunnyCars is one of the cheaper ones. Sunnycars website