Most of the weight issues seem to depend on the builder. If you use a lot of 2x4 lumber and extra heavy plywood floor, etc, your foamie is
not going to be lighter.
Please recognize that a 4x8' piece of basic luan plywood that is 1/8" thick weighs about 9 pounds and you can calculate out some of the possible difference from there.
You also can do a little bit of research for yourself here:
viewtopic.php?f=2&t=56787&p=1035007#p1035007(If you are using Google, there should be an icon in the upper right corner of your screen that will allow you to zoom in and read the charts better.)
That I know of, there are 3 foamies listed amongst the 100+ trailers, Aligator (a lift-top half-standy model), Eaglesdare, and GPW's.
Please recognize that weight is not the only consideration for building a foamie. Among the other reasons are the sometimes quick build, lower cost, and, probably most importantly, the lack of plywood delamination worries. Also, because the foam used is thicker than the customary plywood builds, the increased insulation and lessened noise are points to consider.
I had the privilege of seeing atahoekid's foamie up close and it is remarkable. However, I would call his a hybrid because he has a wooden interior, as does KCStudly's. I think MaryC is building a true foamie. (If I forgot anybody, it was not intentional.)
I hope this helps you in making your decisions.