I believe that feeding right is the basis for keeping pets healthier and living longer. Prevention is key to save vet bill costs and give a great quality of life to your pets.
I chose Oxbow "Cavy Cuisine" pellet food, because it is an excellent quality food at a reasonable price. I have been very pleased with it, and my guinea pigs are crazy about it! (Nope, I'm not affiliated with the brand in any way and am not getting paid to sell you their brand - it's just my honest opinion.) You will likely notice as I did, that the color and smell is better than that of most other guinea pig foods on the market. I have found that buying food online when there is a sale is the best time. I recently was able to get 50lbs of Oxbow (2 - 25lb bags) for $50 and free shipping. $1/lb is a great price for such great quality food. If you choose to buy in bulk, it's important to keep the food fresh, so keep food sealed up in a cool, dark area for storage so it doesn't lose nutritional value. Guinea pigs will eat approximately 1/8 to 1/4 cup of food per day each, so you can get a couple weeks worth of food out at a time to store in a sealed bag or container by the cage for convenience.
One important thing to add about the pellet you choose, it should not have bits of seeds or other things in it. You should give them veggies and some fruits on the side - more info on that here. Buying pellets with sunflower seeds and other things mixed in there is not nutritionally beneficial and they can get the pieces of seed shell stuck in their mouths.
Hay is an extremely important part of guinea pig diet for digestion, and there are so many options! Hay should be available to your guinea pigs at all times. Did you know, alfalfa is high in calcium and should only fed to young guinea pigs or pregnant sows? Timothy hay is the best choice for daily hay. This is why I also chose a guinea pig pellet that has timothy as the first ingredient. Sometimes I mix some orchard grass or meadow hay in there too, which has a sweeter aroma. They love it! You can select any brand of timothy hay, it's just important to find a fresh one with a nice green color and strong fragrance even through the packaging. I've found Oxbow to have the best smell and color I've found at the local stores, so I know it's the good stuff! I recently ordered hay from Small Pet Select online and also have been very happy with that hay. Avoid anything brown/yellowish in color or dusty. A proper diet goes a long way in keeping your cavy going strong for years to come!