In my homebrew campaign, much of it when for the upkeep of ship and crew and to support various organizations and factions they were involved with.
Exploration should involve long travel and significant expense. In lower levels, there should be some benefactor (but "bene" should be in scare quotes) covering these costs.
At higher levels, the party may fund their own expeditions.
At even higher levels, perhaps they have their own strongholds and lands. I've not done much with strongholds in 5e, but I backed Matt Colville's Kickstarter campaign, so I may be in the near future.