Hmm, the best advice I can give is to go to The Tire Rack online. They have the best prices that I am aware of.
Order/Buy Here: http://www.discounttiredirect.com/direct/currentPromotions.do or www.tirerack.com Then take them to the Tire Shop on Halsey (Good Guys/Affordable): http://www.portlandtireshop.com/
Went to Les Schwab....... Costco and this small shop today. God-Damn! They are from $600 to $1000! There were a couple cheaper, but they were shady brands!
I'm just impressed you're asking about purchasing tires. You strike as someone who jacks 'em and leaves the car you stole them from on blocks.