Gardening on the cheap is my specialty!!
I agree with SilentRunning, filling the bottom with rotting wood is a good idea. You could also try calling tree trimming services (or the county road crew,) and asking what they do with the shredded wood chips after they finish a job. Usually you can get them free, or for just the price of the gas to get to your house. (The smaller pieces of wood probably would rot down quicker.) Go to a local Starbuck's, and ask them for coffee grounds, mix them in with the wood chips - you can add many,
many buckets of coffee grounds in there. (If you don't have a coffee shop nearby, try a gas station or restaurant.) Water it thoroughly.
You might try getting in contact with your local 4H or FFA club. There is probably a kid that would
love to let you muck out their stalls!
(Or a farmer that would allow you to haul away his pile!!) Sheep, goats, rabbits, llamas, and alpacas - all of these produce what is called "cold manure." That means there is not enough nitrogen in the manure to burn the plants, the manure does not have to age. Water it thoroughly.
Also, you could try straw bale gardening. If you start
soon, you should be able to get the bales ready in time to use them this year. (Last year I experimented with a straw bale, and I managed to get the internal temperature up to 150 degrees in three weeks. So you'd still have two to three weeks for it to cool down enough to plant in.) Position them over the wood chips, and cut the baling wire after you have them in place. (This year, it might be better to plant in them without cutting the wire. Then cut it at the end of your growing season, and let it rot down over the winter.) Again - Water it thoroughly.
All of that will rot down over the course of the year, so start yourself a compost pile now, and you'll have it to top it off next year!
Hope that helps!