An agent should be able to provide you with a good idea of what the current market rates are for your property, given location, size, access (if industrial), age etc etc
If the lease term (including options) is equal to, or less than, 3 years, an agent can prepare a standard commercial lease for you - my office doesn't charge for this, but some may.
Leases longer than 3 years need to be prepared by a solicitor - usually an agent should try to negotiate terms so that the Lessee pays the owner's reasonable legal fees associated with drawing up the lease. Obviously if the lease is for $10k pa then the tenant usually won't want to fork out for legal fees.
Any retail lease must be drawn up by a solicitor, regardless of the term.
I hope this helps!