Being a contractor / having your own company is not cheap. Its always hard to decide what to charge your clients but a good start is to figure out what your overhead is with just having a company. There are lots of costs associated so here is a list of some of them for the "average" contractor.

Startup Costs
Incorporation (By a lawyer. You can do it on your own for a lot less): $700-$100
Licensing of software required
Hardware required

Monthly Costs
Business Insurance: $100-$200 (basic insurance. not errors and omissions which is more expensive)
Payroll (income tax and cpp. you do not have to pay into EI) : $500-$1,500
Accountants fees (if you are not doing it yourself): $50
Phone: $100
If you are working from home add in utilities, rent, office supplies, vehicle, postage, etc.
Also if you are entertaining clients add those expenses
Note: this does not include the salary you are paying yourself which is a huge chunk of monthly costs.
Total Monthly: $750 - $,1750

Annual Costs
Accounts year end: $1,500 - $2,000
Federal And Provincial Corporate Tax: $3,000-$7,000
(NOTE: Corporate tax will vary depending on income and expenses so this is a pretty broad estimate)
Total Annual: $4,500-$9,000

Total: $13,500 - $31,200 / year

Take this with a grain of salt as these are all really rough estimates and every company is different but it gives a little bit of focus to see what the basic costs are.