I use Nylon Bags for my farm.
You will need small bags to prepare the seedlings and also big bags for the final planting. Small bags like the ones shopkeepers use to package 2KG sugar normally cost about Ksh100 for 200 pieces. Bigger bags can cost as much as Ksh15 per piece and you will require about 1000 of them in a 1/8 th acre farm.
This picture is not my farm, but they look like this..
.
If you are interested in Mushroom farming I would sign up for the online course eLengo is running with The University of Eldoret. I signed up too to learn more!
Sign up here....
https://goo.gl/forms/OOjny5KZCzFiS3Nl2