You can find a portable dehumidifier at home supply stores and other retail chain stores during certain times of the year. Unfortunately, they only carry them during the seasons when dehumidifiers are most needed, so you may not be able to find one at a store ahead of time.
Find a portable dehumidifier online year-round. Most stores have a website and nearly every website will sell you a portable dehumidifier, even when the stores aren't keeping them in stock.
Decide what you need the portable dehumidifier for. If you just need it to remove the humidity from a closet or small bathroom, you won't need to buy as expensive of a dehumidifier as if you're using it to remove the humidity from an entire basement.
Check the amount of pints each dehumidifier holds. Most portable dehumidifiers hold between 30 and 70 pints. This is the amount of water that will fill up in the tray before you have to empty it.
Factor the dimensions of the dehumidifier in with the places you plan to keep it. Words like "portable" and "mini" mean different things to different companies.
Make sure that the dehumidifier has any extra features that you desire. Some of these might include auto shut-off, different fan speeds and an air filter for people with allergies.
Expect the price to vary from as low as around $30 for a portable dehumidifier made for a closet or small room to more than $200 for portable dehumidifiers with a higher pint capacity and more features.