Old backpack strap for the footloop, piece of Pex pipe for the "tether", Ropeman 1 for the ascender attached with a DMM XSRE biner, and some bulk 1/4" bungee cord with a boat snap.
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Takes a little longer to clip in and clip out of than the name brand stuff and may not be quite as efficient, but it gets the job done. And for ~$50 worth of material it's a real wallet saver. Sure the Pex pipe may break, or the strap will wear out, but they are dollar store fixes. The expensive components (Ropeman and DMM biner) will last forever and it's so easy to swap everything out. Paying $150 for something that will be used less than a minute per tree just seemed like a waste to me.