Yep, I made a few holds with this a while back- I think it’s called Bond-Crete and you can get it at most auto supply shops. It doesn’t work out particularly cheaply (although cheaper than ‘real’ holds).
And you will need to work FAST and get the bolt hole in at speed as well- we made about five holds and only one was usable due to either the back of the hold not being flat, or the bolt hole not being made properly . . . so in that sense, not cheap at all. But I bet once you worked out your technique you’d be OK!
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