OK, Ive not used an agency but I do know about them.
Advertising agencies charge one off fees for projects and also do retainers. It depends on how you want to pay. Retainers can be on pre-agreed contracts of, say, 12 months or rolling contracts with a call off term of ,say, three months which means you agree to give them three months notice if you want to walk away from the contract.
The only way an agency will usually demand you pay one way or another is if they think your budget is too low. If your monthly spend is on the low side theyll seek solace in the fact that youre tied in for 12 months or however long it is.
PR in between. 5 hours per month? Out of interest not a pitch, Id charge you about £250 for 5 hours work and that would get you one news release. Speaking bluntly. Most agencies wouldnt bother with you unless you have a minimum of around £1000 a month to spend. Realistically they want £5,000 a month from their clients. So Bills advice about using freelancers is good.
When youre allocating time and budget for PR remember that a PR person just writes news releases the same way accountants just add up numbers
For one news release my minimum service level would include
Research from background papers provided
Background research using Internet search tools as required
Phone interview relevant staff for background information
Research personalised media list
Draft release (up to 400 words) from client brief
Submit draft release for approval
Submit media list for approval
Manage client approval process
Action up to two rounds of client amendments
Distribute to approved media list
Include me as primary contact for further media information
Follow-up phone calls to - up to - five key journalists from the approved media list
Co-ordinate media responses and deal with media requests as appropriate
Forward approved release for client files
Forward approved distribution list for client files
And then theres planning, strategy, media competitions, features, reader offers, evaluation etc.
Design? Track down a freelance designer too. Consider a template advertisement where you pay for the creative ideas and execution at the outset and then ask the designer to simply resize and forward the adverts to each magazine/newspapers specification as required.
Your PR adviser should be able to recommend the best media titles for you to consider advertising in. Although its unlikely he/she will buy the space for you or advise on the best deals. Since youre not buying lots of space buy it yourself.
Consider committing to a minimum spend over 12 months that means planning - and you might get a better deal. Use your commitment to gain favour with the magazine and additional editorial space. (Although this depends on the relationship between ad sales dept and editorial dept on each magazine/newspaper concerned)
To conclude: Forget agencies until your marketing budget is closer to £3,000 plus a month probably more. Track down a specialist freelance designer and PR consultant you like, trust and who crucially - gets you results. Consider giving them a three month trial. Then if it works out hold on to them!!