So I think I found a way to make anywhere between 36k-90k in about 30-60 adventures utulizing the sea depending on how you spend your sea dollars. The first step is to solve the skate park problem with a skateboard. This gives you acess to the three buffs in that zone: Busker Do (At the end of every combat in The Sea you will acquire a sand dollar), Swimming Head (+25% Item Drops from Monsters (Underwater only)), and Familial Ties (+10 Familiar Weight (underwater only)) all for 30 adv.
This is what I have equipped for underwater adventuring:
Hat: straw hat (+10% Item Drops from Monsters, +15% Food Drops from Monsters, +15% Booze Drops from Monsters)
Shirt: Grateful Undead T-shirt (+5% Item Drops from Monsters)
Weapon: octopus's spade (+5% Item Drops from Monsters)
Off-Hand: spiky turtle shield (+10% Item Drops from Monsters)
Pants: poodle skirt
Accessory 1: diving muff (Lowers underwater penalty)
Accessory 2: Baron von Ratsworth's monocle (+10% Item Drops from Monsters)
Accessory 3: makeshift SCUBA gear
Familiar: plastic pumpkin bucket (+5lbs, and +5 lbs of gravy fairy)
edit: i forgot to add the i use a Grouper Groupie as my Fam
With all this plus the 3 buffs, I can garuntee that I'll get 30 sea dollars and usually 6 pieces of fish meat granting me 30 turns of the fishy effect. Once the 30 turns are completed, you can go to Big Brother and and trade in your sea dollars for items that will fetch anywhere from 6k for the seagrease(5sea dollars) to 29.5k for the rusty lamp(20 sea dollars). I haven't tried it yet myself since i'm still saving up for the sushi mat(300 sea dollars), but i believe that my math is correct and i'm fairly certain that the sea items sell pretty quickly.
edit: the rusty valve goes for 12.9k for only 10 sea dollarsand the waterlogged bootstraps are 17.8k for 10 sea dollars putting a 2 day (60 adv) total there at 106.8k
