Fresh Market

Doesn't it just make you want to cook something?

If it's not only vegetables you need, you can buy meat in the section behind the veggies, fruit a few stalls over to the left and eggs a few stalls over to the right.

The vegetables seem fairly inexpensive to me, but if you buy them in the provinces outside of Bangkok, they are even cheaper. During the harvesting season (which rotates through different produce all year long), you can get a kilo of fruit or vegetables for a few baht (about 10 cents US). It all depends on what's in season.