ONe of the things that you have to consider is how much it costs you to live while you are working on a design/show, as this is your livelyhood, and after you get into tech and such it is particularly difficult to work on the next show you are doing.
So, for example, let's say you live in an apartment and pay $500 rent each month. From that you know that you don't want to be making less than $500 per week. If you have to travel to the
theatre for tech, is the
theatre going to pay for it? Is it far enough away from home that you need a place to live and will the
theatre pay for that? If the
theatre is paying for those things then don't worry about it, if not you should make a rough estimate as to what that will cost you and factor it in.
Now consider that the
theatre is going to pay your from the moment they hire you until you complete the show, it is usually some package deal as opposed to a weekly pay. So, if you know that the designing and paperwork
phase will take you say 2 weeks and then tech will take 2 weeks then you know a starting
point of about 4 weeks. Most theatres don't expect the designers to stay around for the run of the show, but if where you are working does you should include that. Also, you should find out if the
theatre has an extension policy. My
theatre pays the designers something extra for every week that a show extends past the original run.
Now, if you go by the model I was setting up, you may want to add a week of fudge room, for your sanity. So that is 5 weeks of work at about $500 per week which brings you to $2500 for the show. It is a starting
point, and it outlines how to figure what you need to make to be able to support yourself.