Then you're under the wrong impression.
I listed the prices of my typical slug purchases above. The cheapest that I've found is at Walmart (of course, when you can find them). The Winchester and Remington 2 3/4" slugs go for $8.75ish for a 15 pack, not cheap by any standard. Both companies have 00 buck for a similar price, also only at Walmart.
Go looking for slugs at your local gun shop/Dicks/Cabellas and you're looking at $1/round minimum.
Birdshot can be had cheap, but is useless at the range. Federal bulk packs go for (once again only at Walmart) $23 for a 100 round pack. That price is more on par with my standard of "cheap" rifle ammo. It's good for blowing stuff up at close range in the woods and would definitelyput downan intruder at <10 yards, but aside from that it's pointless.
I guess it all depends on what you're looking to do with the gun. I don't hunt and I bought my gun for home defense and shooting in the woods. It's a Benelli Supernova Tacticoolness with an 18", no choke barrel that's useless for anything other than self-defense. So just make sure you buy a gun that'sgood at what you intend to use it for.