You really want to eat all of that cactii? Or even drink (or rather, gulp) cactus slurry? It's worth it, to be sure, but be sure you have enough. You should obtain at least over a foot if you're using San Pedro, although I suppose it depends on the effects you want. Some people do well off of six to eight inches. Unless you're a regular kitchen chemist, I wouldn't recommend trying to do a complete extraction and purification. Chemical burns hurt. Trust me. But if you have the expertise and the knowledge of how to use various solvents and reagents, you can end up with decent quality crystalline mescaline. Yum. Better to just swallow the cactus rather than risk blowing something up, including yourself. There isn't a whole lot of nauseau if you do it right.
And I would give you some cactii, but they have some growin' to do! I processed one of them a while back; one hell of a hassle, but worth the effort. Don't get Peruvian Torch, by the way. It nearly always has a lower alkaloid content on average compared to San Pedro.
~Ethno