First, get soil. I go to our local landfill where they offer free mulch and ask for "fines" or fine mulch. It's mulch ground down to a decent soil consistency. It's still "hot" in the huge pile so the seeds are cooked. You'll obviously need a truck or trailer for getting mulch. You can add a little compost but just a little.
Second, get your pots. Bamboo roots need space to grow, so try to get seven gallon or bigger pots. I just started out with old rubbermaid totes and whatever else the neighbors threw out on trash night, and I got the bottom quarter sections of barrels, that were previously upcycled and used for clam aquaculture. Lucky for me, they had a strong polyester screen covering the bottom, preventing any rooting into the ground while offering good drainage. Later I traded fresh cut bamboo roots for professional pots of all sizes and soil from various people including a landscape company.
Now to get the almost free bamboo. If you don't already have a source for bamboo, then place an ad on craigslist with this type of wording. I'm interested in your bamboo roots, or free bamboo maintenance. In my ad I explain my intent and what I do to the bamboo. For example, If you'd like your bamboo plant maintained for free, I will come out and cut out the dead canes, and haul them to the road, and thin out the edges by removing some newer roots. I won't leave a mess behind and I will respect and take care of your property. A lot of people ask for the bamboo to be completely removed while others will let you have plenty of roots for just trimming up their bamboo.
You need a reciprocating saw with a cord. Batteries don't hold charge long enough for bamboo roots. The saw should be a minimum of 8.5 amps. You'll need 9 and 12 inch pruning blades for the saw. A few of each preferably. You can get a new saw for about 35-40 dollars. But if you spend more you get more. I recommend skil or cobalt saws.
When you get on the bamboo, just brush away any debris or mulch on the ground around the bamboo cane with your hands. Pick a cane that's on the outside of a clump with some decent clearance all around it. Make sure the cane has some branches and leaves. The more leaves and branches, the better the roots.
Next stab down into the earth with your saw blade while activating the saw. Start with a 12 inch if it's a bigger bamboo. While keeping the blade buried as far as it will go, cut a square all around the cane, as far as you can up to 10 inches. Square is better, because you don't want to turn the saw while cutting as it will bend the blade.
You will cut through the thin hair roots which are easy, then once you come into contact with the rhizome root, you'll have to apply pressure and patience until your blade passes through it. Once you've completed the square 12 inches deep, remove your saw. Grab the cane and start to rock it firmly in all four directions. It should start to come out. Once it does, pull it directly upwards. It should come right out. If it does, then cut the top of the cane off leaving about four nodes.
If it doesn't then try to rock it and see if there is still more rhizome to cut. Try to tilt the bamboo so the rhizome is exposed and you can get deeper with your saw and cut. If all fails, leave it there. You didn't cut the top off, so it will recover. Go on to the next root.
Do not waste much time getting it into a pot. If you have pots and soil with you, then pot the bamboo on site. Rock the root around while watering it in to the pot. Bamboo roots hate air pockets. Place in the shade for a month or two and keep moist. After that, you can place it in shade with partial sun until its bushy. Once bushy you can safely plant them in the ground wherever you'd like.
If you put them in the ground, make sure you water them daily for a couple of months. Then weekly for a couple of years thereafter until it's established on its own.