We have a material input that produces various different products. So
Product A will produce product B,C, and D. We would like to create a
standard cost system and I am thinking of ways to establish the direct
material std cost. I was thinking maybe by weight. For example if
Product A weighs 3 lbs and products B,C, and D weigh 1 lb each, then
they get 1/3 the cost of product A each. The only problem is our high
priced items are light so we would have high selling prices with low
costs for those items and low selling prices with high costs on the
heavy items. I need a good alternative in establishing direct material
costs for this situation of single input-multiple outputs.

What you have is a classic joint costing problem.  There is no way to
identify the costs of individual outputs since they all benefit from
the cost of the input.   Since you seem to be concerned about
miscosting things you already know the sales value of, you should
consider using the relative sales value method.  That is simply assign
the joint costs of inputs to the outputs in proportion to there
relative sales values.   If you look in any cost accounting textbook
you will find several different alternatives for allocating your joint
costs.