Do you really want whitefish (a specific species of fish; around here it's mountain whitefish) or do you want white fleshed fish fillets which would include sole, halibut, etc?

If you just need white fish fillets then Costco has some good deals as did Uwajimaya last I checked. Talapia in volume can get pretty cheap. Right now the standard decent per pound price for talapia and cod is 5.99 (talapia) to 9.99 (cod). I've seen talapia as cheep as 3.99/# and cod at 4.99/#.

Safeway also has some good fish deals. The circular comes out on tuesday.

Do not fear the non-white fleshed fish. King and Atlantic Salmon are awesome though the only Atlantic you can find is the eco-unfriendly farmed type. Coho is OK (but just OK) and while I like Sockeye a lot it seems easy to screw up. Keta and Pink Salmon suck. Keta is being marketed as a eatable fish but I don't even like it smoked. S'ok in a chowder or cioppino but just.

Tuna is friggin great and you can get albacore here very cheap. It's white-ish... OK, it's kinda gray at times, but still good.

They sell only smoked whitefish, but the cheapest place I've found to get both fresh and smoked salmon fillets is Loki Fish. They sell three places: the Sunday Ballard Farmers' Market, the Ballard Market at 15th and Market Street, or off the docks at the Fisherman's Terminal under the Ballard Bridge.  They're considerably cheaper and it always tastes spectacular.

Even though whitefish is freshwater, you might want to go to the fisherman's terminal anyway. it's cheap and those boys are fun to talk to.

I've also heard that while most folks lean towards fresh fish, a fresher tasting fish is often sold frozen and that a lot of 'fresh' fish is really just thawed.