I wanted to try growing organic herbs on the window, but realized that hydroponic system was too much for me to build and maintain. I did not want to experiment with water filled containers hanging over electrical heater, which is right under my window. Instead, I decided to go for "in-soil" method. I am using various plastic containers from produce, and seltzer bottles as pots.
Materials purchased so far are:
Untreated wood planks and screws for shelves
Jiffy Windowsill greenhouses
Miracle-Gro Organic soil mix
Heirloom and organic seeds from Botanicalinterests.com
Cost:
$40 for seeds (I have plenty left for future crops)
$50 for shelve materials, soil, and greenhouses.

I am attempting to grow Basil, Chamomile, Chives, Sage, Arugula, Kale, Lettuce, Chili Peppers, Swiss Chard, and Cilantro.

Step 1: Shelve

My window sill is very narrow. I used two 2 1/2" wide and 3/4" thick planks with additional support in the middle. The construction is very simple: each side is nailed to brackets (2 screws to the wall for each).

Step 2: Sowing Seeds

Instructions for sowing seeds came with Jiffy greenhouses. The most important thing is not to overwater. Once first green leaves show up, clear plastic domes are removed, and containers are placed on window shelve for a while.
Some useful tips about Jiffy greenhouses from Home Depot reviewers:
http://www.homedepot.com/p/Jiffy-Windowsill-Greenhouse-Kit-5710/100186246#product_description

Step 3: Replanting

When "true leaves" come out, it is time to replant into larger containers. "True leaf" is the third leaf growing between the two initial leaves.
Containers are made to have to have double-bottom for. Second bottom is cut out from the lid, and few holes punched in it to help the drainage.
Containers are also made from Seltzer bottles. Cut each bottle in a half, remove the cap and stuff some paper towel in the opening, and put the top inside the bottom half. Paper towel will filter the water drained through the soil.