One of the cheapest and easiest ways to store food long term is with a food grade bucket. These are usually five gallons, but can come in four or six gallons as well as many other sizes.
You can find these buckets on many food storage or emergency preparedness site's. Of the the cheapest I have found were at Emergency Essentials. But, I beg you not to waste your money on a new bucket. There is a secret to getting as many buckets as you want for free (or very inexpensive). Just call around to some local bakeries. Their flour, spices, sugar, filling and many of their other ingredients usually come in these buckets. Because of this, they end up with a bunch of empty buckets laying around.
The first place I ever called gave me twenty for $1 a piece. Now, if we call around, we are sure to find someone that will give us them for free.
The Bucket - Make sure that when you get a bucket it is food grade. One trick is to look on the bottom of the bucket. It should have a triangle with the #2 in it. It should also have "HDPE", which stands for High Density Polyethylene. This is the only material food grade buckets are made from. If your buckets are not food grade, they can leach chemicals into your food over time.
The Lid - The lid should have a rubber gasket that goes around the inside of the lip. This will ensure an airtight fit.
The Process - There are several standard ways to seal the food in. The first is to use a mylar bag and an oxygen absorbing packet. Place the bag into the bucket and a oxygen absorber into the bag. Fill the bag with your grain or other food item. Fill to about 80% of volume. At this point, some people add bay leaves to deter little bugs. You can also toss in a moisture packet, but this isn't a must. Then seal the bag with an impulse heat sealer or an iron. Make sure the seal is a good one and air tight. Add your lid and store.
I do not use this method myself. This method is intended for storing food for 10 + years. I am a strong believer in using what you have and having what you use. This means using your food and replacing it. Because of this, I do not have a reason to store my food for more than 5 years. Therefor, for many of my buckets I do not do anything besides put the lids on. These are the buckets that I get into somewhat frequently (let me just add here that a nice bucket opener is a good thing to have). For the items that I won't be getting into any time soon, I use dry ice to seal the buckets.
Place one ounce of dry ice for every gallon (five gallon bucket = five ounces of dry ice) into the bottom of the bucket. Pour grain over the ice (you can also add a paper towel, or something similar, if you don't want the food to possibly get burned from the cold). Leave about an inch at the top. I add a few bay leaves. Then slide the bucket over the top, but don't seal it. When the bottom of the bucket starts to warm up, you can seal the lid. Watch it every 10-15 minutes to make sure the bucket doesn't start to bulge. If it does, burp it (open the lid to let the gasses out).
I add some packing tape to the lid and write with a sharpie the date I sealed it and what food item is inside. Now store and enjoy in a few years.
Keep in mind that the best place to store these buckets are in a cool, dark, dry location that is safe from bugs and rodents. For every 10 degree drop in temperature, they say that it doubles your storage life.
Good luck and enjoy.