Is it more expensive to fly in October or November

least expensive month depends on the destination. like if its more popular in the summer it might be more pricey to fly.
Usually plane tickets go up in price during the summer because children are out of school and more people then start to travel.I think it's cheaper to book airlines flights during the winter months.in november Tickets tend to be cheapest after everyone has go on vacation. September and October tend to be the off-peak season since lots of families with children will not be traveling due to kids being in school.
the best time to fly to Vancouver, Canada is Probably late October to early November , and again from December to late April. The very months when no one wants to visit because the cold weather in the northern hemisphere and it isn't Christmas when everyone wants to visit relatives.

From October to February is the main tourist season, pricing for flights to Australia is much more expensive.There are few if any sales or promotions during this season and the cheapest flights are available only if you purchase your tickets early.
January and February are the slowest time of the year (as in less travelers). The price of tickets (unless you're going to a ski destination) generally are lower. The airlines quite often offer deals during January and February to get people in the air. But it also depends on where you are going. it can be expensive if you are flying to Asia since lots of people fly home to celebrate Lunar New Year.
there are quite a few sites that you can search that will likely give you the best prices available. check out the website and you will be able to compare prices on all the reputable travel sites in just a couple minutes.
http://www.kayak.com/
http://www.orbitz.com/
http://en.momondo.com/
http://www.expedia.com/default.asp
http://www.farecompare.com/
http://www.farecast.com/
http://www.airfarewatchdog.com/
http://www.tripadvisor.com/