We're building a small skills course at the moment at a mates place in a spare paddock, despite it being flat we have used several existing piles of dirt to build some pine NS structures out from, plus turned one into a tabletop.
We've spent exactly zero $$$ on it, just used wood we had lying around at work that no one wanted.
We even built a seesaw from bits of pallets (awaits flaming), with plenty of reinforcement its damn strong and currently resides between two trees. It comes down to time and effort more than money.
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