I am in a similar situation. My land is in Tehama county, CA. in the wine country. Hops used to be grown here, but gave way to grapes and nut trees. Anyway, I have done a lot of research and basically the factors to consider are:
$5000-$10000 per acre for trellising, irrigation (drip system) and rhizomes. This is a one time start up cost. After this you have maybe $500-1000 a year in expenses such as rental equipment, labor, repair, etc.
Labor: basically anything over an acre and you can hardly hand pick unless you have a lot of cheap and skilled laborers. Harvesting the bines and renting a picking machine may be an option in the Willamette Valley?
The upside is that if you get a license, you can sell to brokers or brewers at $10-40 a pound...at about 1400-2200 lbs per acre, it could be a great business.
Dave Willis at Freshops gives a bulk rate(over 100 I think) on hops rhizomes. Contact him.
Crannogales in BC has a downloadable guide on small scale hops farming. Check it out.
For me, I am just doing a test plot this year of 1/4 acre. If all goes well it should produce around 500 lbs by 2010. The temptation to go bigger is there, but the hops market is going to be crazy over the next few years, and with planting up everywhere, there may be another bust (low prices) after this boom?
Going organic, which is my plan does allow a grower to charge more, and supply a market segment that is crying out for locally grown hops.
Good luck!
Tim