standard dose=100mgs?? yea I don't think that would even be close to enough. and your probably getting ripped off, I havent heard of anyone selling molly in 10$ increments.
I'd double check just to make sure he said or you heard it right. I've had mis communications with dealers before and I was like "wwwhhhhaaaatttt????". but it turns out he said something different than what he meant or I mis heard him. so double check and ask to see it before you buy.