It all depends on the type of fabric. Wool varies from $5/yard to $100/yard depending on a number of factors. The wool used in most "traditional" kilts is typically $50-80/yard depending on source and wholesale vs. retail. The cost of wool has also gone up. The reenactement store I have bought most of my wool from has increased their prices from $5.99/yard to usually $9.99/yard for basic wool (more for "specialty" wool) because of increased wholesale cost.

Wool blends are often cheaper than 100% wool as well.

Most reputible Belted plaid kits are expensive because of the expense of the material inside. Others, however, are rip offs.

In short, it pays to go to a reputible source, like Celtic Croft or the Tartan Museum.

By the way, recently I bought some clearance fabric for a belted plaid at $1/yard, but it is acrylic and ight not even be washable. For me its a "disposable belted plaid."