I hope its a Stihl, I have a Stihl 460 Magnum with a 20" bar, 25" bar, and a 28" bar. I just picked up a Stihl 650 Magnum with a 20" bar for $250. Good deals are out there, but you have to wait for the right one. The Stihl 650 will be wearing a 32" or a 36" Stihl ES Light Bar when I get some more money in. Im keeping the 25" on the 460 as it is best balanced with it. However being that you are younger than me and I am 20, they do get quite heavy. So for right now I would reccomend something smaller like a 029 Super which has enough power for a 20" bar, but is not that heavy. Or look for a MS 260 Pro or MS 261 which are around 10-12lbs and handle up to a 18" bar but have enough power to pull them.
Here are some pics of my saws:
Stihl MS 460 Magnum
Stihl MS 650 Magnum
Where I will be cutting for a long long time across the street: