Yes it is very expensive. I use the whole Canna range from Rhizotonic from start to finish, Cannazym, Coco A+B, Bio Boost during flower and PK13-14 but not as directed on the label - says week five only, I use it over weeks 4 and 5. I flush at the start of week 6 and stop feeding at the end of week 7 but continue the Cannazym and Bio Boost till the end.
Bio Boost is not as potent as Boost but the results are the same although you use more of it. So while you save in price, it probably costs more over the long run. The result is it knocks about a week off budding. As I grow mostly master kush at the moment, that helps since 9 weeks is normal for MK, that way its ripe for the picking at end of week 8.
Due to the fact Im budding in a tent I also use Yield Masta's 'Sudden Impact' to keep those unruly master kush under control as they can get away on you if you let them.
What mls per litre are you feeding your plants at using Coco A+B? Is that because you are using the coco slabs or something?
Added: Just read what you said above about the 50 litre pots.