Answer: an arm and a leg at a time.
Better answer: hourly, fixed fee and on contingency.
1. Hourly Rates
An hourly rate is $x/hr, usually billed in six minute increments. Most lawyers use computer software (with digital stopwatches) to keep track of the time they spend working for a client (e.g. Carpe Diem). At the end of the billing cycle (e.g. monthly) thee lawyer's program spits out a set of “dockets” and the client gets a bill for 5.2 hours x $x/hr.
2. Fixed Fee
Depending on the work, it might be possible for the lawyer and client to agree on a fixed price for the work to be done. This is common for real-estate, incorporations and other predictable areas (see FlatLaw.ca for more examples).
This arrangement is sometimes called a "flat rate" or "block fee".
The scholar of lawyer pricing may want to read the US Supreme Court case that banned bar associations from setting fixed prices for legal services.
Contingency fees are fees proportional to the success achieved (e.g. a 30% cut of the damages). This billing method is commonly used in personal injury and class actions (15-40% of recovery is typical).
One of the challenges with contingency fees is that ultimate success in a case might not happen for years. While the case meanders through the justice system the lawyers are financing the case (including expensive expert witnesses).
Contingency fees have been around for a long time but were only officially permitted in Ontario in 2004.