I plan on building your pen as I like it's entire concept. I like to drag my paddocks periodically with harrows. By using electric ribbon I will be able to loosen it and lift it, allowing me to go underneath the top board. I pull the harrows with a quad or riding mower. Pressure treated posts here are about $6 plus $5/post to have them punched in but the $250 overall cost sure beats $1800.