Chickens!
Chickens are the least expensive animal to start with. Chickens multiply quickly and you don't have to buy anything special in order to make them breed. You can buy a chicken one day, and the next day you've got an egg to hatch into another chicken.

The Chicken Coop is located just to the right of the Cow barn. You can buy your first chicken from Chet for 1000G. Chet will require that you have planted 9 bags of grass back behind in the pasture area. After you buy your chicken remember to go back to the Coop to feed it. You need to feed your chickens every day in order to produce eggs. You don't have to brush your chickens or shampoo them. The only special treatment they can get is you picking them up.

If you have a friend who also has Harvest Moon 2, you can trade chickens via the computer at Mary's Library using your Gameboy link cable. If you receive one of your friends chickens and then go check in your Coop, you'll notice you have a Golden Chicken! Golden Chickens of course lay golden eggs and the eggs sell for 500G each. If you want you can sell your Golden Chicken to Chet. He'll give you 10000G for just one Golden Chicken! You can also hatch more Golden Chickens out of golden eggs.