Also, does anyone have advice as to the best format to work with recruiters?
It's hard to say. Independent recruiters vs. agency recruiters have different deals and earning potential, overhead and the like. Good, independent recruiters make a lot of money.
Are you thinking about the cost of hiring a recruiter vs. the cost of using a 3rd party? Recruiting has to be a core competency of a growing company. And the network of existing employees is the best place to look for new talent. I know it's a time sync and pain in the @ss, but it's super important that you get hiring right.
If you are going to use a recruiter, you need very clear expectations in terms of what skills, experience, requirements you are looking for and stick to them. Also, do everything in as timely of a manner as possible. You should also note, recruiters have best customers also. If you don't have very specific and unique requirements, you can assume the 'best' candidates you'll get are the ones better customers have passed on (doesn't mean they aren't right for your company, but just an FYI).
Lastly, very few recruiters have strong networks they've cultivated. Most of the time, they are just more ambitious / aggressive pounding the pavement and social media.
http://www.ewherry.com/2012/06/the-recruiter-honeypot/
http://www.ewherry.com/2012/08/the-best-recruiters-followup/
The standard fee charged to companies is 25%, though that is often negotiable. At Hired.com we charge 15% (20% of which goes back to the Engineer/Designer/Data Scientist when they get hired).