Im pretty impressed on the domain name you have, but quite doubt about your SEO service. I don't see your website (www.seo.com) for keywords such as - SEO,SEO service,Search engine optimization......... Hope you list your site in SE for that keywords
It's depend on you. You have to decide what you need form the SEO company if you only need few work then they will charge you as per the Job. So Every company will work fopr you as per your budget if your budget is $100 for this months SEO you have to decide what you need then contact to SEO tell them your budget they will suggest you. Suppose you need 1000 Directory submision + 100 Pr submission + 100 Blogcommenting you don't have to pay $5000. It's fully depend on your budget
You can also try guru.com as well for finding professionals for various roles including SEO. Plus you can see all the past jobs and experience they have. Be careful of picking anyone without a "rating" , try and do your due dilligence as well.
I would be carefull asking that here! You will prob get lots of people suggesting themselves, or even worse, pretending to off up a website they 'know about' but is really theirs. I would be inclinded to search google for a decent firm, ask 4 or 5 for detailed quotes, what they would do etc... At the end of the day, if an SEO firm cant rank for their chosen keyterms (check their page source etc) then avoid them! Any SEO worth their fee will be happy to chat to you about what they would do for you etc... -