Well, you have to understand the economic value that is specific to your area and then somehow find a happy median between that and what you can afford and what you feel the value of having that extra set of hands is worth to you.
I would say, and I do follow my own advise, that if an employee is going out with me to help, then he can't cost me more than 20% of the days total income. Otherwise I feel more as if I have a partner rather than an employee. In actuality, I shoot for about 15% or less per man. Now that would be different if he was part of a two or three man crew, with myself being absent and available to go out and do other business related matters.
You have to figure what your billable hours come to and multiply that by what you normally charge per hour or what your average hourly income from cutting is. Needless to say, I charge hourly for just about everything except mowing, fert., aeration, etc. .... things that can be priced by the sq.ft. ... not there is anything wrong with "per job pricing" but this is what I feel more comfortable with.
If two workers can cut $90 per hour, and you are paying them $10 each, then your payroll is about 22% of your hourly income, and leaves you to go out and do other work, estimates, or sit at home and watch TV .... whatever. If you were to go out with just another guy, then your payroll would be 11%, but with drive time and loading/unloading, "BS" time, etc. .... you realistically wind up at more like 15% with you and another guy, and about 25% with two guys out working and you free.
Here on Long Island, it is rough finding someone to work for less than $10 per hour, or $100 a day. Regardless of what they will be doing, I really do not think you will be able to go much lower than $8-$9 per hr. and find a hard working and trustworthy individual.