Expiry: Unknown Report Expired Deal
United is having a sale for various cities, including Buffalo, to Vegas. Availability is limited, but if you look around you should be able to find dates in April and May for around $200 all in.
Sample dates include April 10 to 17.
You can check on the united.com website, or look at united.ca for prices in $Can. I'm unsure when the sale will end.
Edit: As found by golfer29, this fare is available on selected dates for all of this year and early next year. Use a tool such as Kayak or ItaSoftware to look for dates.