No, US Airways is no longer an option as they're no longer an Aeroplan partner.
$250 + 83,000 miles seems awfully steep for coach class in what I consider to be a cheap market. Cancun in July is reasonable from BUF. I suggest waiting to see how much the fares are going to be. If you're determined to use miles, I would wait until the 330-day mark to see if you can grab UA reward seats to save on both miles and fees.