I don't see it as being an item that gets cheaper at any point of time during the year...unlike winter blankets that go on clearance at the end of winter, or fly sheets the end of summer. You might be able to catch it on sale, but that would require watching tack stores for prices.
I've never seen them go on sale here. Our tack shop only has three types, two are not certified and the Aierwear I have is certified, I bought it for around $250 at Big Dee's. You could buy used if you find soemone selling one in your size.