applying by own than you save atleast USD 2000 of consultancy (depend on lawyer some charge less and some lawyer charges more).
cost is depend on how many people you are migrating (you + dependent/s) becasue visa fees and landing fees have to pay for you and dependent.
another cost of courrier's , your IELTS or french exam fees, medical examinations fees for each applicant, PCC's, photocopies, notary services, if interview is there than travel expenses, yes dont forget that you need POF(proof of funds) and that you need to show depend on how many applicants you are.
Table of POF:
http://www.cic.gc.ca/english/immigrate/skilled/funds.aspTable of Visa Fees & RPRF fees:
http://www.cic.gc.ca/english/information/fees/fees.aspOMM