One thing that hasn't really been separated out in this discussion is the difference between pyro cone and temperature. It is comparatively simple to reach a temperature in the yellow white range in a propane furnace. That is mostly a function of BTU in and volume. Cone is a function time at temperature or heat work. I know that most readers of this forum make that assumption know this but for the casual or newer member it would be well to be more explicit.
When people say that running cone 6 in a Raku kiln would me unreasonably expensive in terms of fuel I take that as recognizably true. If one assumes a Small Orton cone this gives a temperature of 1255C with a temperature rise rate of 300 C/hr.
Cone 04 on the other hand seems more achievable as a small Orton cone is 1098C @ 300 C/hr. Personal experience tells me that the time an effort to go from and orangish yellow to yellow white heat is a lot.
All this is in aid off is the point that Raku is more Art and Craft and Experience than many other parts of custom made ceramics.