I’ve got a slackline that I have to use an A frame and ground anchor with. We only have one tree.
Mine are from slackstar (German brand). Putting the ground anchor in was hard work, but the set up is ok.
If you can avoid using the ground anchor and A frame, it will be a lot cheaper to get started and we tend not to leave it out overnight, as the A frame is wooden.
It’s great fun and really good exercise. Good luck with it.