There is some good advice above, especially from Gabriel.
Generally when i'm quoting
SEO work I look at:
1) How well optimised the site is currently in terms of onsite. This can work both ways - more problems = more work, but also easy fix problems can equal a ranking jump without much difficulty.
2) What the type of keywords you are looking to rank for - how competitive they are but also if they are locally based (ie "widgets sydney") vs nationally focused ("widgets" on google.com.au) or international ("widgets" on google.com)
3) The strength of your competition. For some words/phrases there are no strong competitors and whoever is at the top is there because noone has done a good job. On the other end of the scale there are some keywords where nearly everyone on the top 5 pages has worked hard on
SEO, and it's just that competitive (think mortgages). Most fall in the middle.
One hint about the "per month" stuff, this is where a lot of
SEO companies will get you. There is ongoing maintainence to be done, but normally it will require more work up front and then less work as maintainence. Prices should reflect that - a lot of
SEO companies take a bit of a hit upfront and work more than they are paid to get you to the top, but then do very little work ongoing but keep you paying month after month.
Also beware - I have recently come across a neat trick that a lot of
SEO companies are using that allows them to "turn off" your link juice and send you dropping in the rankings if you stop paying. I'm NOT going to let out what it is on a public forum (I don't want to be hated), but just be aware that this sort of thing is out there. For the record I don't use this tactic and all links built are genuine.
Pricing wise - To be blunt, anything under $100 won't get much "real" work done and will generally just pay for someone to run an automated linkbuilding program that won't help much.
Generally my prices would range per month initally anywhere from $100 - $2500 depending on how much work needs to be done and how competive the industry. Let me know if you would like a completely no obligation quote on your work. - Email
matthew@marketingweb.com.au