It depends how accurate you want to make it.  If you are happy to lose a little detail (really not too much), wrap the original in baking foil, holding the joins with masking tape.  Add one more layer.  Press them in very firmly.  If there is a gap, put another piece over and hold it in place with more masking tape.
Then begin your paper layering, up to about six layers, allowing to dry after each two layers.   When all is totally dry, cut carefully around the middle.   Fine, sharp scissors might be best to avoid scoring the original.
Pull the two halves together with masking tape.  It doesn't matter if the foil stays on the inside.  Add more paper layers until the whole thing is as firm as needed.
If you want it to have a bit of bottom weight, tape a well sealed small bag of sand or similar inside.
DavidO