I just got a bucket full of strawberry plants free from someone cleaning out runners from his bed. He posted it on CraigsList. I've also seen on CL or Freecycle people giving away raspberry bushes and such when they need to thin out their plants.

Second freecycle and craigslist. There can be a lot on there if you live near a city. If you're out in the country, you might want to take your own cuttings. Things like blackberries and elderberries can be found in the wild and grown from cuttings or seeds without hurting the wild plants. Also relatives, friends, or neighbors gardens might produce some finds. In the spring walmart will probably have some cheapie plants, not sure what kind of quality they are though. I purchased one (silky dogwood) from there and it lived although it never really did much. Also there is the plant trade on here. I've had some cuttings and seedlings mailed to me for postage and they did good.