I'm going to jump on the get yourself some cactii bandwagon. Because mescaline is wonderful and I've yet to find something close to it. And it is well worth doing at least once.
As far as extractions, getting mesc out is easy, getting pure mesc out is beyond what the average person can do. You need chromatography to separate it. But the impurities are inactive and nontoxic (it's stuff like N-methylmescaline, and N,N-dimethylmescaline). If you have any questions about the extraction process feel free to ask.