The best thing you can do is just buy 1k or 2k and use the 100 Gold Pulls, that hopefully someday will reset every day like the DMM Version does. Because that would be the best ratio you can get, it would be 1$ or whatever currency you use for one pull. Not 50$ for one 11 Pull and 14 extra Gems. It wouldn't pay off immediatly, but since there is nothing to rush in the game, besides event maps, it would definitly give you something over the weeks.