You can buy a basic 15' ladder stand from BassPro for about $55-65.

We've built some basic stands.

3 16' 2x4's and a chep pallet from work.

2 16' 2x4's for the ladder and the other for the ladder steps. Attach to the pallet for the base with lag bolts.

We raised it to the tree with ropes and used a lot of rachet straps on it.
Burried the 2x4's in the ground about 2' for stability.
Still not as sturdy as we'd like.