The stores I've been use a combination of their in-store mats and player's mats. Using mats brought in by players is fine, just make sure you measure them to make sure they are 36"x36" and make sure that mats stay on the same table and that players can't choose which mat they want to play on.
You could also get a 36"x 12,000" roll of Kraft paper at Wal-mart for $50 and just cut out 36" sections and tape it down to the table and then throw it away at the end of the day, that's enough paper for 330 mats.
Our TO got a deal on fabric with a starfield printed on it. The big pain was cutting that whole bolt to regulation size squares.