From personal experience and talking to other freelance trainers the type of industry a client is in has a huge bearing on their ability to pay. For example, it is much easier to charge higher fees in the professional services sector than it is in the public sector.
If you are asked to write a proposal in an industry in which you are unfamiliar it’s a good idea to ask around people in your network for information on the ‘going rate’.
Or ask the client what they are expecting. It may not be what you want to hear but it can save time in the long run.
As you become more experienced you will get a feel for what you can realistically charge within each sector and then you can decide whether it’s worth pitching for the work.