World of Warships: Legends

Self explanatory. Other than premium ships, the cheapest and fastest to get would be three cruisers, a destroyer, and a battleship from each country. Just keep progressing the cruiser line until you can unlock the first battleship, being careful not to sell any ships. Then buy the unlocked destroyer and battleship. Then repeat for the other country. Premium time, xp boosters, and credit boosters can speed this up.