I think every attorney does it differently. Some want a retainer (basically a deposit they bill against.) Others charge a flat per-year fee for certain basic services and bill hourly for others. And others just bill you each month for their services.

Most attorneys will give you a flat rate for some services, like development of agreements, terms of service, review of legal agreements, etc. Depending on your specific needs and complexity, you could probably get a Terms of Use agreement in done several hours, since most experienced attorneys will have boilerplate they can modify. If it's a customized partnership agreement or something, expect it to take longer.

From my experience, an experienced adult industry attorney seems to be in the $200-400 per hour range. Price is not necessarily correlated with quality.