If you have an old refrigerator out in the garage or in the basement, you own one of the cheapest, most effective wine storage coolers available. It's easy to convert and can store several cases of wine at near-perfect temperature and humidity requirements. You could spend more than $500 for a storage unit of similar size.
Remove all the shelving and drawers from the refrigerator. Using a mixture of 1 gallon of water to 1 cup of bleach, clean the refrigerator thoroughly and leave the door open to air dry for at least 6 hours.
Place a thermometer, one specifcally designed for refrigerator use, inside. Set the temperature control on the refigerator to the fourth setting from the coldest. Allow the refrigerator to run at this setting for 12 hours. Check the thermometer. You want the refrigerator to achieve and maintain a temperature of 55 degrees. Keep checking every 12 hours until that temperature is reached.
If you want to use the freezer unit of your refrigerator for storage as well, repeat steps 1 and 2. Set your freezer at the warmest setting and then adjust it every 12 hours until you reach a stable 55 degrees. Some older freezer units won't be able to achieve this temperature. If that's the case, you can either keep the freezer compartment empty or use it as a normal freezer.
Storing your wine can be as simple as ordering a modular wine rack that fits the interior dimensions of your box. An alternative that will allow maximum storage space and let you add on as collection grows is to purchase a section of 4-inch PVC underground drainage pipe at a local home improvement store. The pipe comes in a variety of lengths. Be sure to get the type with holes. Cut the pipe into 8 inch lengths and stack them into the refrigeration like logs and place your wine inside the pipe sections
Controlling the humidity inside your wine storage unit is important. It must remain moist so that corks won't dry out. Storing bottles on their sides will keep the cork moist on the bottom, but there could be some shrinkage on the top. Avoid this by placing a small, stainless steel pet water dish with several inches of water in your refrigerator. The water will evaporate maintaining the humidity level in the box. Check the water level every week and clean if necessary.
Wait to store your wine in your new unit until the temperature has had a chance to stabilize. It won't hurt the wine if you store it in there right away, but doing so will make the refrigerator take longer to achieve the 55 degree temperature. That will add a bit to your electricity bill.