GTA, 10HP for a snow blower is the minimum around here. Anything lower you'll have to push and shove it around to do the job... Been there, did that... It's not worth it in aggravation, frustration and with all possible problems an overstressed blower might have. Nothing worst that blowing an engine when at -30 and 90% of the driveway left to do... As I said, been there, did that... Look at about $1200 for something of quality. I'm told Ariens are among the best.
http://www.ariens.com/products_snow/s_deluxe_group.aspx
As far as a contractor or a blower, well, it depends:
1- How much time can you afford for snow removal?
2- Are you in good physical shape?
3- Contractors have other customers, how early and fast do you need to get out?
4- Lots of snow mean lots of space needed to put it. Last year, some contractors with 4X4 and blade ended-up piling the snow from driveways in the streets. This is illegal in most cities and caused the owners of the driveways who's snow ended-up in the street to get nice fines of a few hunderd $... Some streets were so narrow because of this, emergency vehicules didn't fit anymore! So you have to ensure your contractor have access to some kind of backoe or truck-fixed snow thrower. That ensure the snow will be left on your lot or carried to a dump site. Of course, this usually demand a premium over a simple 4X4 with blade. This is a problem you'll likely not face with your own snow blower since you can plan at the beginning of the winter where your "snow dump" is on your lot.
4- Most if not all contractors will now have a "maximum precipitation" clause. I heard of a few guys last year who almost went belly-up and they don't want to take any risk anymore. This coming winter is supposed to be pretty much like last year from what I heard...
5- prices will vary widely but, for a quality, well equipped contractor who have commercial insurance (a blade can easily rip a house corner, you know! Try to have an "under-the-table" guy to reimburse that!) you can estimate over $300, and it still depends what size of driveway, how difficult it is to do and, of course, if you want the guy to also do balconies and sidewalks by hand...