It usually works that a lawyer will take a retainer of some amount and then bill their hourly fees as they go against that amount. In Texas, it is common for retainers to be $2,500 to up to $25,000 in some very complex cases.
Unfortunately in the volatile world of family law, clients aren't always willing to pay their bills if their backs are against the financial wall. They begin to think that the lawyer should share in their bad decisions or bad luck regarding their family law matter. This is why for financial survival, most attorneys have made the decision to ask for up front retainers. As the hourly fees are drawn against the retainer, the clients will have to "replenish" the retainer after it drops below an agreed minimum amount.
Clients should receive regular bills so they can see what activity is going on in their case and how much retainer has been used. It is common practice that at the end of the case, and amount remaining in the retainer is refunded back to the client.
On the note of money, if you are on an hourly contract with an attorney (I'm not talking about flat rates- which are rare in family law) beware of attorneys who try to get you to agree to any non-refundable retainer amounts. They may try to convince you that this amount is for the "privilege" of hiring their wonderful firm. These egocentric lawyers, usually from the biggest firms with the fanciest offices, (read: most overhead) think there can charge you simply for the honor of paying them their hourly fees (which are probably grossly exorbitant). Such "nonrefundable retainers" have been found to be a breach of attorney ethics unless they are very clearly spelled out. Even then, they are looked on with disfavor by the majority of honest attorneys. You should pay for the work done on your case. PERIOD. You should not pay a penny less, but you also should not pay a penny more either.