Actually Katmai (Brooks Camp) can be a very cheap trip if done right. You can use AS or DL miles to get as far as King Salmon. Then you only have to pay the +-$200/person round trip floatplane cost from King Salmon to Brooks. Then camping is $12/person/night. I have done a week-long Katmai trip twice. Each time the total cost including flight, camping and food was well under $500. Most people spend over $600/person for a day trip. Their loss, my gain :-).
Agreed. Best way in is through Silver Salmon. Stopping over there, SS has a few places to stay and do some fishing. Then do a day trip into Katmai. After a couple of hours of watching the bears grab the salmon at the falls, you will get bored and go back to fishing. The trip to Brooks/Katmai still remains one of my favorites.
One other option, is check out Silver Salmon Creek Lodge. I have never stayed there, but stayed at a native corporation camp nearby and had plenty of encounters with bears.