One of my clients (also a programmer) has recently decided switch his main development tool from VFP to Delphi. He has also decided that he would like to keep me on, have me learn Delphi, and keep cranking code. He has a couple of months in Delphi behind him, and many years in Fox, but relatively little experience with VFP. Most of my value to him as a consultant was application strategy and guidance in VFP in general.

Obviously, I am not currently as productive in Delphi as I am in VFP.
My question is how should I deal with rates when programming in Delphi? My client has suggested that we begin at half of my VFP rate, and increase by a pre-stated amount per-month. Neither one of us, however are sure of what is fair.

I am always eager to learn new technogies, and so part of me looks at this as a golden opportunity. Another part of me wonders if I am screwing myself. A lot of the things in Delphi, and VFP are the same, like form design and data design, and I can spend a significant amount of time doing them, and making half of my former rate, even though production in these tasks is close to the same rate.

I spend an average of 50 hours a month on this contract.

I would really like to hear somebody else's take on this, to help me through a strategy here.