If I had to pleat my own kilt, I'd be in serious trouble. Celtic Croft can sell you the filly and for an extra $50, sew pleats in it for you. I think it's worth the fiddy dolla just to not end up in the middle of the living room floor in tears.

Edit: check out their "clearance" tab. They have a few major bargains on feilidh beags there. The selection's limited, but something may catch your eye.