The employer/sponsor will need to pay a fee to UKVI of £199 to assign the CoS and may also have to pay the Immigration Skills Charge.
The employee will have to pay the applicable visa application fee (which for those applying for a skilled worker visa for up to 3 years is £247 per person and more than 3 years is £479 per person, unless the employee is from an eligible country (namely Austria, Belgium, Croatia, Republic of Cyprus, Czech Republic, Denmark, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Luxembourg, Malta, Netherlands, North Macedonia, Norway, Poland, Portugal, Slovakia, Spain, Sweden or Turkey) in which case the application fee will be automatically reduced by £55. They will also have to pay, the biometrics fee and, in most cases, the Immigration Health Surcharge. Some employers choose to cover all or part of these costs.