Even a casual kilt is not restrictive. I have a couple from SportKilt (I wanted to put my toe in the water before spending large bucks on a really nice one, only to discover I didn't like it), and the only restriction you ever feel is around the middle, and that's no more than a pair of jeans would be restrictive.

As for an inexpensive fighting kilt, I'd recomend taking a look at the sites already mentioned (SportKilt, USA Kilt, Stillwater), and see what appeals to you.