I have these ingredients

[karpes]

I have been using 60% cheap cow manure compost ($1.30 #40 bag) and 40% Peat with fairly good results but I am trying to improve the mix this fall and spring. All will be grown in 5 gallon grow bags/buckets in the greenhouse this fall and outside in the spring of next year
Here is what is available to me from Lows and free.

3.8 cubic feet peat $10
2 cubic feet pine bark compost $3.02
Rice hulls (not composted) unlimited supply
Horse stall bedding (raw uncomposted) unlimited supply
Fired clay pellets (light concrete mix aggregate used in hydroponics) $32 per cubic yard

I know the horse stall bedding is going to be hot so I am having second thoughts about using it without a chill period but maybe just a little?
For the outside containers I plan to continue using the Mittleider method with timed irrigation but in the greenhouse I will be using fertigation with 20% run to waste.
The cow manure compost/ peat mix, if my math is correct runs me less than $1.50 per 5 gallon container but I believe that with your help we can come up with a better mix at about the same price or even less.
I have experimented with coco coir with excellent result but it is just too expensive to use when you are filling 40 containers.
Your thoughts?
Karpes

[dice]

You could probably add 20% rice hulls with no downside.
It will take a long time to break down and act like adding
perlite or coarse sand (provide more air space and drainage
to the mix).

If the horse stall bedding is mostly manure, and if you let it
compost for 6 months, you could probably replace the
composted cow manure with it entirely. If it is mostly wood
shavings, it would take a lot longer and need some added
nitrogen source to compost to the point where you could add
it without nitrogen draw down. If it is mostly straw, 6 months
of composting would still probably have it ready to use,
but it would be lower in N-P-K, especially nitrogen, than
if it were mostly manure (you may need to adjust your
liquid fertilizer ratios).

[karpes]

Thanks Dice
The use of the hulls alone will cut down on the expense. The horse stall bedding is mostly wood shavings so I have been cautious when using it, but it has worked well in raised beds
Karpes

[dice]

Mostly horse manure can compost in less time, I have heard
as little as 2 months, especially in your summer heat. Some
people turn mostly fresh horse manure into their garden as
little as 2 weeks before planting in it. I figured 6 months
was safe.

Mostly wood shavings with some manure mixed in is more
of a long term project to compost it enough for container
mix. (I bet if you till it into your beds in spring, it still looks
like wood shavings by fall that same year. That would be
the case here, anyway.)

If you are using artificial fertilizers, you can get away with
using uncomposted wood products if you add a lot of
nitrogen. I remember an old formula for azaleas that was
in some ag project description from 40-50 years ago. They
dug a hole, maybe 5 or 10 gallon size, filled it with a mix
of sand and sawdust, and larded on the sulfate of ammonia,
enough to give you 4' long dandelion leaves if you used that
much on a lawn. (The formula also had moderate amounts of
superphosphate and potassium.)

Figuring out just how much chemical nitrogen to use for a
10-gallon container full of wood shavings might take a lot
of trial and error, though.