If your business is thinking of using a temp agency, there are several factors to consider. Do you need a large supply of unskilled workers for a job with high turnover? Are you looking for a few highly specialized workers in technical fields? For a high volume of workers, it might be best to contract with several temp agencies to ensure access to all the workers you'll need. However, working exclusively with a single agency can sometimes allow you to negotiate a discount on the agency's fee. If your temp needs are more modest or specialized, there may be other advantages to building a relationship with a single agency. In rare cases, a single contract can become so important to a temp agency that it actually has a full-time liaison working at the client company's facility to oversee the temps.
The specific cost of hiring a temp agency to provide workers varies tremendously. It will depend on the jobs being filled (unskilled jobs like basic office or light industrial work pay less than technical jobs), the cost of living in the region, the agency's particular standards and fee structure, and discounts or deals worked out as part of the contract. Employers always pay the full wages earned by the temps, plus some percentage above that. A good temp agency will be upfront about the wages and fee structure, so you know exactly what you're being paid.
The process of using a temp agency is relatively simple for workers. It's just like applying for a job: You submit a resume (possibly online, depending on the agency), fill out an application, and have an interview. For unskilled positions, this meeting can be very brief; for higher paying jobs, it can be more like a full job interview. There is often a screening phase during which the agency may conduct a background check or require a drug test. Once you've been accepted into the agency's workforce, you'll be offered one or more jobs that fit your skills if there are any immediately available. There may be a delay of several days or weeks until something opens up -- the more general your skills or the positions you're willing to work, the easier it will be to find you something that fits.
Your pay rate is typically determined by the temp agency, and it pays you directly. If you're trying to turn the temp position into a full-time permanent job with the employer assigned to you, you may discuss that with the company. However, the temp agency often negotiates temp-to-perm positions themselves -- your supervisor at the agency will explain how that's handled.