I've got a fairly large vegetable garden, and spent a year looking into this, and ended up making my raised beds w/o timbers, just soil heaped up and the slopes protected by weed barriers.

There aren't a lot of good, inexpensive landscape timbers out there - opportunity stuff like seeing somebody ripping some out of a subdivision entry planting and you ask to take them, or the old guard rail posts when they re-do a fence along a highway, that kind of thing.

You might look into cinder block.

Timothy,
I was scrolling through Cragislist this evening and there's a posting under Farm and Garden, the 2nd page of 100 postings, near the bottom of the page for used landscaping material - $7 (erie). It says they have 4"x4"x12 treated posts for $10, 6"x8"x6 treated for $6.50 and 8"x8"x8 creosote posts for $7. It's JB at Ideal fencing corp. They have a separate posting above it for used guard rail. They have a phone # listed, but I don't know if it's ok to list here, so I wont. I don't know them, but thought you might want to take a look. I hope they have what you need. Good luck!
Barb