It shouldn't cost you anything to hire a personal injury attorney, not out of your pocket anyway. However, they're not free either.
Most personal injury lawyers charges what's called a contingency fee. That means that they're paid contingent upon getting you a settlement. When your personal injury case is settled and you are paid by the insurance company, your attorney gets a percentage of that settlement money.
Using a contingency fee is great because it saves you from having to spend cash up front, and it gives your lawyer the incentive to work towards getting you the biggest settlement.