Oh this is easy. First of all, don't buy a hybrid and don't buy new, you'll get a lot more for your buck going "lightly used", with a stronger bike. I have a couple of thoughts, both based on my personal experience.
Option 1 - For a road style setup, there are lots of used Trek 520's and Novara Randonee's around, check on Craigslist, espec in Calif.. Plan on around $600 for a 5-10 yrs old in bike good shape possibly with some extras. Mine is 10 years old and I would head across the country on it tomorrow, but I see many that are newer in that price range. Your bike will likely come with racks, but if not budget $100 for them and $2-300 for lightly used or new panniers on sale somewhere, espec this time of year. There are tons of panniers on Ebay for cheap - I got my like-new Arkels there (thanks Greg!) That leaves you a little change for a tune-up on it or spares, etc. You can definitely do this within your budget, and the great thing is you can sell it afterward if you want and not be out much change at all.
Option 2 is even cheaper. Buy a used 10 yr old rigid (no susp fork) steel mtn bike like I just did for under $200 in great shape (Trek 970, chromo, lugged frame with XT components). Many of these are hardly used and there are lots of them so you don't need to take the first thing you find. If you get a top of the line one it will have excellent components, rack eyelets, and of course they have great gearing already. Have it serviced, check chain, cassette, and the wheels for true and bearings. New Continental Town and Country tires for $50/
pr are pretty much bulletproof, great traction on/off road and roll well on pavement. Now for less than $400 you have a great all-around bike that will ride well (steel) and go the distance, even some off road if it's not too gnarly. You may want to add a higher stem and bar ends for comfort. On mine I added Jandd Extreme front and rear racks for $130, and a set of panniers (4) as mentioned is around $2-300. Your total investment would be under $800, leaving a bit left over for a better seat or clipless pedals if not included.
Either bike will take you anywhere, the road-style setup will be a bit faster and cover longer distances, the converted mtn bike will do fine and add a bit more capability for dirt roads, mild trails, etc. Or you may just like the flat bar setup better. Both bikes are far stronger than a modern, cheap aluminum hybrid with wheels and components that are not up to the task of carrying a load for long distances.
Have fun!