It's be easy enough to buy some 36" PVC pipe and bury it. Then just have one spot at each end to shoot from and change targets out....unless you ran some cable and pulley set up for targets. Even then some serviceability access would be nice.
They have them in 14-foot pieces for around $212ish apiece. 11 pieces per 50 yards would work out to $2,340, plus the holes at each end and burial/backfill cost.
Using SDR35 sewer pipe, not couplings are needed, goes together with gasketed bell ends.
Plastic Pipe 36SDR35GJ14 Pipe Size 36 Inch x Length 14 Feet PVC SDR35 Gasket Joint Sewer PS46
www.fwwebb.com
Just a thought.
Mike