I can't advise you on how much they are at those pet stores because I live in the UK and we don't have them here.
Parakeets/budgerigars can be sort of loud, but not as loud as other birds such as lorikeets. If you get a young budgie, you may find that for the first few weeks he will make a high pitched 'screeching' noise - as this is how they call their parents. They'll grow out of that though.
When you get your budgerigar, remember that he or she is going to be very scared at first (what with leaving its friends and seeing a bunch of strangers), so make sure you help it settle in. Don't make any sudden noises, and avoid getting loads of people to crowd around the cage. Talk to him or her frequently, so that it can get used to your voice. After a month you can then start thinking about training your bird.
In terms of housing, make sure you get a cage big enough for your parakeet. Ask the people at the pet store for advice about this.
For more info:
http://www.justbajan.com/pets/birds/species/budgies/index.htm
http://www.letstalkbirds.com/budgie.htm
http://cfhs.ca/athome/budgerigars/