Oh my, considering how much work I went to I'd say $300 is worth it, especially if it includes cleaning all the toys and clothing. If an item that she touched has touched another item, it has to be cleaned so it amounts to an amazing amount of cleaning that has to be done, and quickly if you want to catch all the nits. I spent almost 24 hrs doing non stop cleaning and we have a small house.
If the cleaning service only is for household surfaces, make sure you clean ALL your clothes, coats, hats (esp. hats), mittens blankets, sheets, pillows, and towels even the ones you have in the linen closet, and all the toys, especially if they are soft. I recommend taking them to a laundromat as it took me over 30 loads to wash everything which amounted to 6 loads a day for 5 days.
Also don't forget to clean or replace all your brushes and combs. Get a cheap one to use during the infestation and replace it when you are done.
As PP mentioned I too would recommend cutting unless she is really really attached to her hair. My DS's have really curly hair and getting the nits out was horrid took soo soo long to do and they didn't have long hair, just really thick. So after I combed the first time, I basically gave out buzz cuts (I have a clipper and always cut myself). We never had a recurrence but DS' friend, from whom we got the lice

, didn't want to have his hair cut so his mom gave in but after two weeks, despite the constant cleaning they kept coming back. At this point she insisted they too cut the hair and lo and behold, no more lice.
Also, make sure you clean not only your house but your car, especially the seat where she sits. People forget about this one all the time and then wonder why they keep coming back. I found a whole bunch of them lingering on the seats.