when my hen was about 3 months old, i built her next boxes. i took a tall round bean crate and cut it in half and used both of the halves in the house they sleep in. i nailed them to the wall so they wouldn't tip over and put some pine bedding in the bottom and a little bit of timothy hay from my rabbit so they were nice and comfortable. and she's been laying eggs in one of the boxes since she was 8 months old. you don't have to buy a nest box, just find something or build something thats sturdy enough and big enough for your hens.
i think its like 2 hens per box or something like that? i only have one hen, so i have an extra box. good luck!