In reply to Chive Talkin\':
I did something similair during lockdown to hang hammocks and string a slackline up.
Dug two 30cm square holes a metre deep then put in 3 metre long scaffold poles, postcrete and a bit of hardcore in there then a pole across the top as a cross bar.
Bish bash bosh, jobs a good un.
Great for the hammocks and sturdy enough to string the slackline from one pole to a tree on the other side of the garden, about 8m long.
Probably cost around 100 quid for the poles, fixings and postcrete.
Edited to add costings.
Post edited at 00:05