Two different things share the word retainer. The common one is an advance on fees: you send $2,500, the firm holds it in a client trust account, and it gets drawn down as they bill time against it. Unearned money left at the end is generally returned to you, and the engagement letter will say so. The rarer one is a true retainer, a payment just to keep a lawyer available, which is usually not refundable. If nobody said which one you're being offered, ask, and ask whether they'll bill you again once the $2,500 runs out.
Hourly means you pay for time recorded, most often in six-minute increments, so a four-minute phone call still costs you a tenth of an hour. Flat fee means one price for a defined piece of work, like reviewing a residential purchase contract or drafting a lease.
Rough ranges, and these swing hard by market: a purchase contract review runs a few hundred dollars up to around $800, a residential closing handled by an attorney is often several hundred to a couple thousand and is required in some states and not others, and a boundary or title dispute is where retainers in the thousands show up because nobody can predict the hours.
Before you pay anything, get the engagement letter and read the scope paragraph. It says what's included, what's excluded, and who does the work. Paralegal time often bills at half the attorney rate, and a firm that pushes routine drafting down to a paralegal can be cheaper for the same result.
