Hi Eric,
Personally, I wouldn't offer different hourly rates to the same client. I would do everything I could to establish my value to THEM and stand behind it. If you are a powerhouse of expertise at $200 and I have a problem that isn't THAT hard that I need a $200/hr consultant, then I would find someone cheaper than you. If you come in and say that you can do an easier problem or not participate as much for less per hour, then you just demonstrated that your time isn't actually worth $200/hr (to you and me both). In which case, you can offer a "blended rate" that may be more like $150 and in this case, you have just shown again that your real value is not that high. Check out "million dollar consulting". My best recommendation is if you can demand $200/hr, then you should be finding work that pays $200/hr and not spending time working for half that. Hope that helps! I realize you may have a unique situation here. In that case, I would again consider a lower rate where the client will hire you for both types of work. You need to provide a dollar amount that is attractive to them but take some time to really consider what it costs you to be doing work for less. Establish what YOUR time is worth to you and don't go under than unless its for strategic positioning.
V/R,
Gene