The reason is
supply and demand. Cards that become scarce in the
supply pool and are only found in select locations are charged at high prices because they know they're the only ones that have it. Your best bet would be to go to a large chain store or an establishment that's already been around for a while. More often than not they'll exactly what you're looking for at a lower price because they have so much of it that they need to sell it off to make a
profit (which in't too hard for them because they already have a large income and surplus of cards and money coming in). You could always try ordering online but if you want to pay the shipping and handling then that's a different story.
The best advice i have as far as card collecting is to buy up the not-so popular cards that you believe retain value. A lot of times its the commons and uncommons that tend to rake in money because of their usability. Also waiting till certain cards fall out of rotation would be good since tournament players usually only see the value in a card as far as STANDARD goes (modern is for the more casual players in my opinion). Do some trading with seasoned veterans in the card playing community around you and they'll be glad to teach you what they know and maybe even have access to the stuff that most people would of forgotten about.