In answer to your question 'what sort of services does a 'press officer' provide and how much does it cost', another (and perhaps better way of looking at it) is 'what do I want to achieve by investing in my PR?'
So I would suggest thinking about;
What do you want to achieve?
Who do you want to target?
What expertise/resources do you have available in-house?
What external/additional support might you need to help you achieve your objectives?
You might for example not just need someone to help you generate quality media coverage in your target media, but also someone who can help with social media and copywriting.
So put together a brief outlining your requirements and then think about options for obtaining your resources - you could look at employing someone on a project or permanent basis, or commissioning a freelance or agency.
Rates you will pay will depend on someone's expertise and experience, where you are based, the type of work involved, whether you are employing someone or commissioning an agency/freelance.
The Chartered Institute of Public Relations (CIPR) has some useful advice on commissioning PR support. I would always suggest if you go down the freelance/agency route or checking to see if someone is a member.
As a member, practioners need to demonstrate appropriate skills/experience and sign up to agreed standards. There is also an arbitration process, in case things go wrong.
http://www.cipr.co.uk/content/find-...plier/selecting-and-managing-your-pr-supplier
Good luck
Helen