Budgies make their own seed, therefor: Budgie seed.
Actually, there is no such thing as budgie seed. What the shop sells you, is a mixture of millets, oats and sometimes other small seeds. Budgies will eat any seed they can open up. You can collect the seeds from grasses and ribwort and sesame and sunflower, and oat grass, and finger millet, and all the other things growing where lawnmowers have not destroyed all. Any seed small enough will do, even evening primrose, cabbage seeds, mustard, dang, they eat like mice.
Some budgies even nibble on fruit, but I don't see them get as excited as when I, for example, bring a handfull of chickweed, or smutsgrass, or quickweed, carrot tops, soft green grasses, thistle flowers, anything soft and juicy, but NEVER FEED ROOTS TO BIRDS. Too many are poisonous to birds. Think Naturally now; how many birds have you seen dig after roots? Me neither. Dig for worms, yes, even bugs or small animals, but not roots. Yah, sure, quote me the rare and almost extinct Booligordian Carrot Cockatoo, that eats only beetroot. Bet you don't have one in your cage. If I had one, I would plant beetroot all over. But for now I stick to small seeds, soft greens and lots of fresh water with a small crystal of Aloe Ferox in the water. It turns the water brown eventually, but sometimes a stir helps to disolve it. All birds seem to have immediate benefit from this. In a small cage with limited variety of food, one of those mineral blocks they sell you at the merchant in innocent life is essential. If you are too lazy to harvest fresh food for your budgie, at least buy him something to nibble on for minerals. We at Greenpets much prefer the fresh greens way. It is Natural Rearing with Naturally Raw! food to support a Natural Living health conciousness. That's the Greenpets way. Go see the GREENPETS HERBAL for more edible greens to feed your birds.