I take my daughter to a lice removal specialist. She does a thorough combing to remove the lice. 2 weeks later you return for a follow up to check for any lice that might have hatched from missed nits. If there are any lice they are removed for no additional cost and another follow up scheduled. I have had to use the service twice over the years and neither time were there an lice at the follow up. For me well worth the $100 fee. I don't have the patience to perform the type of thorough combing required and certainly would not get them all in one combing.
We did this ourselves and it worked well. I think this is the best approach. I guess you can try combining with some other natural approaches suggested in the comments.
Another advantage of these services is that the daycares trust them, so it limits the time you have to keep your kid out of daycare. This can save way more than $100 (depending on what your childcare backup solution is)
Sorry, I'm completely lost. Daycares? i.e. schools do you mean? And what do you mean that they trust these services? I must be getting this completely wrong, but surely you're not saying there are schools which exclude children who've had nits unless they've got a receipt from a $100 hair comber?