Well start with your current salary and determine the hourly rate that you are paid. Remember to include benefits/fringe rate.

Then factor in the work or expertise that you are bringing to your client. Remember the client will think it is worth less than you do.

You need to know what point that the “job” becomes profitable or worthwhile to you. Use that number.

35-50 an hour
same as anything that is freelancer or contacted. depending also on your type of work.