If and when my brother and I get together I will be able to tell you more but I don't think a 6'6" person would have much of a problem in many RV's today.
I can tell you how to find out though.. The how is universial, the when varies depending on where you live.
Attend an RV show. Here in S.E. Michigan we have two biggies every year, One in Novi, the other Ford Field (Detroit), There is the humungous one in Quartzsite every january, there are RV shows in Las Vegas and in most of the major cities
This gives you a chance to price RV's, usually the lowest price for new you will see all year, View floor plans, and bang your head against the headers if you are taller than my not-so-little brother (6'6.5") (I'm only 6'3" but I'm older)
Now, some areas have good deals on lovingly used RV's too,, More on that in ohter threads