The Marudai I have been using so far was made from an old milking stool with a hole drilled in it (cost: approx. $2 from a second hand shop). Recently I found a three legged plant stand made of wood. The legs are straight down which is an improvement on the slanting ones of the milking stool which get in the way. I still have to make the hole, but the cost of this marudai will be about $3.50 so it's quite affordable really.
One of the members of my weaving guild came up with a great bobbin solution, she use the porcelain guides used to carry 'shockwire' (I'm not sure if that's a
correct English word) round fields to keep the cattle in. They're almost bobbin shaped and about25 gr. in weight, but the centre hole allows you to add a weight if necessary. She use a wide earthenware pot as a marudai. (In the U.S. insulators on telephone lines are similar to this but probably larger, I believe some braiders have used them successfully as tama. Janis)