First off, does anyone in your house use any nonstick cookware? If so, you'll need to get rid of all of it and replace it with anything but nonstick. If nonstick surfaces get hot enough, they release fumes that will kill your bird, regardless of how far they are from the kitchen. You'll also need to replace any harsh cleaners you use (basically anything that isn't specifically labeled non-toxic and biodegradable), as budgies are very sensitive to smells and chew on everything, and you don't want them inhaling or ingesting anything that could hurt them. If anyone in your house smokes, they'll have to quit doing it inside. I don't know what that'll cost you, so you'll have to figure that out yourself.
A healthy, tame budgie from a reputable source (not a chain pet store or BYB) should cost about $25-50, depending on whether you get a wild-type or one of the color mutations. Be wary of people charging less. Chances are their budgies are unhealthy, poorly socialized or both.
You'll need to keep Kwik-Stop on hand in case of injury. It's $10 for 1.5oz of powder at Petsmart. If the cage you buy doesn't come with food dishes, you can get a set of two uncovered food & water dishes for $2-24. (Don't use covered dishes; many birds hate them so much they'll starve to death rather than eat from them.)
You'll need a carrier cage for transporting your bird to the vet -- just a small, portable cage with a perch. Windy City Parrot's carrier cages for budgies are $11-12.
Your budgie will need at least two perches of different thicknesses to help keep him or her from getting arthritis. Never give them sand, sandpaper or concrete perches. Rough perches that claim to file their nails don't actually do anything but abrade their feet, which is painful and can result in skin infections, and concrete perches will give them arthritis. Natural branch perches are best, so long as the wood is budgie-safe. For a table of plants toxic to budgies, scroll down to the end of this page: http://chirpykeets.webs.com/food.htm Wooden dowels, rope perches and plastic perches are also good. They should also have a swing. Petsmart has some pretty good wooden perches for $4-6, and a nice parakeet swing for $3.
Be prepared to spend about $200 on the cage your budgie stays in most of the time -- they're small, but they're very active and need lots of room to hop around and play in to stay healthy and sane. The key things to keep in mind when selecting a cage are:
1. Bar spacing should be 3/8" to 5/8", ideally about 1/2".
2. It should be made of stainless steel or wrought iron with a non-toxic powder coating, as your budgie will chew on his or her cage constantly, and most other cage materials are toxic at that level of exposure.
3. Stay away from cages with fancy roofs, as your budgie could get a leg or beak caught in them and seriously hurt him/herself.
4. When selecting the cage your budgie stays in most of the time, get the biggest cage you can afford. Once you know what to look for, you can check Amazon, Ebay and Craigslist for better prices on a good cage.
So, upfront costs:
Cage: about $200
Carrier cage: $12
Perches: about $10-25
Swing: $3
Kwik-Stop: $10
Food & water dishes: $2-24
Cuttlebone/mineral block: $3
Budgie: $25-50
Total: $265-327, plus the cost of replacing nonstick cookware and harsh cleaners.
As for recurring costs, they need about $20 per month worth of toys. Birds need checkups from a good avian vet (not a regular vet who happens to treat birds, I've heard so many stories of regular vets inadvertently killing birds it's not even funny) at 3 months, 6 months, 1 year, and every year after that. Expect to pay about $50 for a checkup if your bird is perfectly healthy, and more if he or she needs some sort of tests or treatment.
As for food, they should have pellets or a pellet mix that doesn't have millet or any kind of seed in the first 5 ingredients -- seeds are high in fat and low in the nutrients birds needs, and budgies are prone to fatty lipomas, so this is especially bad for them. They should have a little seed to prevent boredom, but it shouldn't be more than 5-10% of their diet. Out of the foods Petsmart carries, ZuPreem is the only one I'm comfortable recommending. A 2lb bag of ZuPreem for budgies costs $12, and I'd estimate they'd eat 3 tbsp per day, which means you'd be spending about $206 per year on pellets. The cost of seed and treats varies widely, and it's a pretty small part of the budget, so I'll let you figure that out.
So recurring costs:
Toys: $240 per year
Food: $206 per year, plus whatever treats and seed you want to give them
Vet care: at least $150 for the first year if you get a baby; at least $50 every year after that
Total: $596 for the first year, $496 every year after that, plus the cost of seed and treats and any vet treatment the bird may need.