Check out some of HBT's wonderful sponsors in the vendors forum.
If you do 5G batches, you probably want the 6.5G buckets at least for primary.
If you do 8G batches, you could potentially split them into 2 HD or Lowe's buckets. Most people don't use those because they are an odd size for batches - for 5G batches, you need bigger.
If you want a 8G batch all in one fermenter (keep in mind that will be much tougher to move), you could try a 10G bucket...I think I saw some at Northern Brewer.