Hello and welcome to BYC !!
Personally my hens have large pens. The ground slopes and it's very free draining. That said winter can get muddy so I get a large bail of straw delivered which costs me roughly £30 and will last me until spring. (I have 40-50 chickens)
I use a good quality hemp...
I use hempcore for inside the coop and nesting boxes. The one I buy has a eucalyptus oil in it which I'm told is good for breathing and conditions feathers. I don't know about that ..
I buy it because it's easy to pick poop out of each day, it's absorbent, smells nice, cushions their landings...