This will depend on who you hire. The best ones charge more because they produce better results. You should probably be wary of those that undercharge.
As a general guideline for lawyers, expect to pay between $500-$1500 per month on average for high-quality Google Ads management. This may be arranged as a flat fee, a monthly fee, a percentage of ad spend, or a performance-based fee.
Make sure that before hiring any Google Ads professional(s), you have a clear idea of the breakdown of costs: what the campaign management fees are and what you’ll be paying to Google. Only then will you be able to budget for your Google Ads marketing effectively.
If they produce the right results for you, anything you pay an agency or Google will be dwarfed by your returns.