Ring of steps is used at height instead of a platform. Some are marketed as a climbing method, but I've never heard of anyone using them that way.
You'll need the following at minimum. Please do your research on equipment and climbing methods. It's better to save up for proper gear to keep you safe or hunt from the ground than risk your well being if necessary.
A saddle - Recon sling is probably the most inexpensive commercial saddle. I have one and like it, but a sling style does differ significantly from a single panel saddle in several respects. Prior to so many commerical saddles being offered, a sit drag backed up with a rock climbing harness was always the goto budget friendly option. Some guys still use it and swear by it. I know you said you didn't want to modify a sit drag, but I didn't know if you'd consider it if all you really had to do was wear a rock climbing harness .
Tether - There are a lot of different options here, but whatever you go with you, you want static climbing rated rope.
Prusik Cord - What size to get will vary depending on what you decide to use for your tether. Wesspur.com has a lot of options here. I like professionally sewn eyes personally, which you can also get through Wesspur.
Climbing method - Hawk Heliums are probably the most budget friendly option here.
Platform or Ring of Steps - You need something to rest your feet on. Ring of steps will likely cost less. I haven't used a ring of steps personally, so I don't have any recommendations here.
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