There are sources (especially on the East Coast of the USA) that carry the tartans in wool material. The average cost at a shop that "knows" you is anywhere from $2 to $10 per yard. Naturally, you're restricted to the availability of the tartan on-hand, but it's usually in quantities that are good.

At those prices, you can offer-up a casual kilt for the $90 range and still make a nice profit for the business. A machine-sewn traditional at $200 is still a nice margin. The beauty is that the customer gets wool... and there's no mistaking wool for anything other than a kilt.

You need to look at sources other than the Fabric Shops. They have a profit margin that makes the material outlandish. Look for the fabric suppliers and closeout resellers in your area. Look for a fabric/garment district in your nearest big city. do a little homework and you can make yourself a kilt for EASILY under $50.