Having an agent gives you a point of contact when you need a binder listing a client company as a named insured. Which is typical for General Liability. The agent can also provide documentation for Worker's Comp coverage too.
Finally, an agent helps find alternatives when there are changes at renewal time...every year. The agent is a person with whom you can have a business relationship. Business insurance quickly becomes non-fungible once you get beyond General Liability.
And be glad they are demanding you have it. It’ll save your ass if something goes sideways.
Cost wise will depend on your limits but expect to spend $600-1200 on base E&O depending on your company risk profile. General liability is usually lower. And cyber can be cheap to crazy depending again on risk profile.
Price goes up as limits and risk increases of course (they should have told you what they expect). Generally always get quotes for multiple limit levels. I found out going from $1m to $2m annual was a small increase in premium so took the increase in limits.