MDMA is stable in water. Take a water bottle and empty it. Add back 10 cap-fuls (as in the bottle cap, not a gel cap) of water. You could also use shot glasses, but the bottle cap works just fine. Dump 1 gram into it and make sure it completely dissolves. Now you know each capful of water that you pour out (filling the bottle cap) is 100 mg. If you want more granularity, you could dump the gram into 100 capfuls of water and dose yourself with 14 of them to get 140 mg. It's a bit of work and not good for filling gel caps, but it is a cheap and relatively accurate solution for not having a scale.