I am looking for an online store (preferably) or a store with a physical location in northern New Jersey (if possible, otherwise central works too) that sells either tatami or beach mats (they can be combined to get a similar feel to tatami) for cheap, for the purpose of tameshigiri (cutting) practice.

A friend of mine can buy two beach mats for $6 (no shipping costs). Most people who do cutting say that two beach mats roughly match one tatami -- so that's the kind of price range we're looking at.