I love 99% of the work I do, except for the 1% that is fee discussions. Below is the logic why it is so hard for designers to do work for free. I know that this blog is read by many independent professionals, you are more than welcome to link to it if you need to.
  • You pay for a design service, rather than hours of labor. Designers bring with them years of experience, they create a story for you to tell that was not there before. The design of the actual slides does not take the time, it is the iterative design process that you as a client are taken through. You purchased your story, a different mind set than buying slides, or buying hours.
  • Like in any other (larger) business, not all top line revenue is profit. Designers buy computers, software, books, printers, office infrastructure, Internet connections, phone lines, cars, go on holiday, need a pension, rent an office, and pay taxes just to name a few of the expense items.
  • Design-as-a-service on a variable cost basis deserves a premium. Most customers cannot afford to hire a full time, highly experienced and talented designer (the cost is too high, and they do not have enough work to keep her busy throughout the year). In exchange for offering design services on an as needed basis, designers expect to be compensated for the inefficiency of not being able to get paid 100% of the time. Negotiating projects takes time that cannot be charged. But the result of this model: a win-win for both parties. 
  • If you cannot agree on fees, that probably means that there is a mismatch of expectations on both sides. In today's interconnected world (cliche alert) this is not a problem. Among the thousands of designers out there, there is probably one that fits the client's profile. Among the thousands of clients out there, there are other one's that fit the designer's profile. Both sides just need to move on.
  • Asking a designer to get paid once you managed to raise money six month from now (and not get paid if the client failed) is the same as asking a stranger in the street to hand over hard cash as an investment in your business. The designer might agree, but it is an investment decision. Does she believe in the concept of your business, and is she compensated for the risk she is taking like any other investor would? Clients need to realize that asking a 1-person design firm to put in cash in their business is different from asking a large supplier to do the same. In the designer's case, it is her own money, in case of the big supplier, it is "other people's money"
Most of the time when I have to descend into this type of discussion, the project in the end does not happen, somehow it did not click between me and the client. Luckily this does not happen that often. 

In case you have not seen it, you should check out this great flow diagram: Should I work for free?

A last piece of advice to designers, do not compromise on the quality of the work when a client puts pressure on the budget. Either take the financial hit but do your art as good as you can, or do not do the project. The client will not understand it when you say that this is not the sort of quality you usually deliver. You are as good as the work you delivered in your last project.