They have tightened up massively now on non Europeans applying to work in the UK under sponsored visas. The entry wage level is above 30K unless the migrant can come in on a highly skilled visa. There are also restrictions on the type of jobs that can be offered as well i.e you cannot offer something like a general office admin employment even if the wage level being offered satisfies the requirements of the Tier Level of the visa that the applicant is applying on.
As Twix123 has shown, the info from the Border Agency will help you to understand the requirements.
Yes there is a cost to become a sponsored employer, the last time we applied it was around £300 per employee, this was a couple of years ago though and it could have gone up since then. You can also use immigration lawyers to submit an application on your behalf, but expect to pay in excess of £1200 to £1500 dependant on who you use of course.
Thanks Sue