Hey there CP, The buckets will work although they won't allow you to spread your PVC as wide as you could if you were to use an 18 quart plastic dishpan.
You can get them at the local dollar stores or Wal-Mart for 2.00 each and once your concrete has hardened for a few days you can push down on all 4 sides and pop them off and reuse 'em.
If you fill the tubs up with quik-crete it will be plenty to sink the PVC. PVC is the easiest of all to sink. Try not to mix the cement too soupy because you'll have trouble getting the pvc to stand up on its own.
If you have mixed sizes of pvc I would put your largest diameter in the middle. Don't crowd 'em together either. Nine or ten pieces at the most per bed. I usually put mine in 10 feet of water so I cut most of my PVC 5 or 6 feet long.