where can I get a cheap one?
Thanks
I don't recommend a cheap one, but if you must, try Canadian Tire or Toys R Us. They will have the essentials...2 wheels, a frame and a seat, a cheap brake system and a cheap gear shift mechanism. It will be a heavy clunker made out of substandard alloys, it will shift gears roughly, it won't be as enjoyable to ride, it will wear out more quickly, but it will be cheap.
The cruisers will have higher or more more curved handle bars and less distance between the seat and the bars, so that you are sitting more upright. Its more comfortable. The hybrids have bars more forward or lower and more space between bars and seat so that you are leaning forward and lower. That makes for a less wind resistance (you can go faster and farther with less effort) and lowers the center of gravity. That will help with balance and manoeuvrability. That's good if you hit a patch of loose gravel on the trail, or if you have to steer around potholes, etc.
If you go to a bike shop, they can explain this type of thing to you and recommend the bike that would be best for you. If you go to Canadian Tire, you will get a high school kid with a summer job that doesn't know anything about bikes, you will save $100 - $200 and end out with a piece of shit for a bike.