Presuming that on the [url=https://roll20.net/compendium/dnd5e/Expenses#toc_4]table for Expenses[/url] the price for mead is roughly equivalent as what it says ale costs.

Note: using Waterdhavian currency:
Platinum piece: "sun"
Gold piece: "dragons"
Electrum piece: "sambar"
Silver piece: "shard"
Copper piece: "nib"