Using somat's estimate of 49" on a side, it would roughly weigh the same as 49^3/100 cu in of solid wood. Given a range of 0.01-0.03 lb/cu-in for pine, and choosing the midpoint: 23.5 lb.

Very portable.

(Yes, it's cotton not wood, but the weight of solid cotton is hard to find, and probably not much different.)

Cross-check: bills are apparently ~1g apiece. That predicts $1M in $100-bills is 20.8 lb. Very close.