The cost retainer is refundable based on the amount that is remaining after the attorney pays expenses related to the litigation such as postage, copying, summons and service processing, parking, tolls, etc. Cost deposits are kept in a separate account and is separate from the attorney's fee.
In your example, Lawyer A seems to be willing to advance you these costs and possibly bill you at a later time. Lawyer B wants you to cover these costs up front.
Court filing fees are always paid by the client.
The retainer is what you pay the attorney for his/her time/expertise. Filing fees and costs are separate.
Lawyers can charge any kind of fee they want (except contingency fees) for a divorce case and while hourly billing is standard, alternative arrangements like flat fees and retainers are also very common.
Whether a retainer is an advance on future payments or something extra in addition to the future payments will vary so you need to talk to the lawyer to make sure you understand what they are asking for.
It sounds like Lawyer B is thinking $500+$1200=$1700 total fees to Lawyer B and they see the court filing fee as a separate thing in addition to their fees.
The fact that Lawyer A's fees are different from Lawyer B's is based on the fact that each lawyer charges different fees. When buying an item in a store, you do not expect every single store to charge exactly the same amount for the item. Why do you expect that from lawyers?
J Charles Ferrari Eng & Nishimura 213.622.2255 The statement above is general in nature and does not constitute legal advice, as not all the facts are known. You should retain an attorney to review all the facts specific to your case in order to receive advise specific to your case. The statement above does not create an attorney/client relationship.