there aren't alot of dive travel agencies that do stateside dive trip packages. Most of us book everything separately, on our own.
since you say you are in Oregon, and want to travel to places you don't need a passport...
Florida, southeast coast (Ft Lauderdale-Jupiter) has great diving in your pricerange
Florida, Keys (Key Largo) has very easy shallow dives and also several wrecks
Florida, cavern country - tons of springs to dive as recreational diver or move up to cave cert
North Carolina coast (Hatteras, Morehead City, Wilmington) has deep wrecks and sharks
California, Channel Islands (boats out of Santa Barbara, Ventura, Long Beach) fantastic kelp forest diving
California, Catalina Island land-based (take ferry over and stay in hotel) great shore diving and boat diving around the island's kelp forests
California, San Diego - boat diving to deep wrecks and also kelp forests
Hawaii... (Kona, Maui, Kaui) lots of options but it is more expensive
Hawaii, liveaboard (Kona Aggressor) probably about the same price as land-based once you pay for food and transportation, but a bit higher than your budget
check out a few websites:
South Florida Diving Headquarters
Florida Keys Diving with Silent World
CONCH REPUBLIC DIVERS
NC - Olympus Dive Center
Discovery Diving Co
Spectre dive boat, Channel Islands, California
Great Escape Boat
Catalina Scuba Luv
Waterhorse San Diego Boat Dive
Big Island Divers
Jack's Diving Locker
Lahaina Scuba Dive Maui
these are just a few websites to check out. There are TONS of dive ops to choose from. California is probably where I would recommend you go for most bang for your buck. It is cold water but in summer (July-Oct) you can expect water 60s-70s and tons of fish, kelp, fun diving. Florida Keys would be my second choice recommendation for you.
robin