You're an in-house SEO in need of outsourcing services. You could go to the big names, but you get big price tags. When money is an issue, you have to seek lower priced alternatives. This is when its vital to properly assess a good SEO vs. a bad one.
SEOmoz has a great list of questions to ask a prospective SEO firm. Actually, the story is pitched to answer them before you start charging for services, but it's a great list to field prospective consultants and agencies.
The one question I would add to the list is: What are your thoughts about PageRank? I'm shocked at the answers I get for that one. For the record, here is my two cents on Google PageRank.