It's $2000 for a Commercial Float or group, $250 for a Community Festival (which probably wouldn't include Kumoricon since it's paid membership) and $250 for a non-profit Float or marching group.
If we can pull the $250 non-profit, it wouldn't be a bad idea.
For the Commercial Float, it requires some assimilation.
$2000 = 60 registrations
Total attendance of the Starlight Parade (est): 250,000
Now think of 3500 random people perfectly representing a set of bell curves. Of those 3500 people, how many are likely to take interest in a cosplay group? Of those, how many would be likely to remember such a float out of 2 hours of fantastic floats present at an event? Of those, how many would take the initiative to find out more about what that float represented? Of those, how many would take an interest in attending the event AND paying the cost of membership? Of those, how many would be able to actually attend the event?
1 of every 3500 individuals in attendance would need to register for three days at kumoricon to break even. 1/3500 doesn't sound too bad, but you have to compare that to existing advertising.
Kumoricon's memberbase draws a significant majority from High Schools and Colleges, and individuals in the 14-22 age range. If 15% of the population of Portland is within that age range, then roughly 1 of every 1000 people within that age range attends Kumoricon. To gather further data, ask some people within that age range if they know about kumoricon. Try to find a figure out of 20 or 50. Multiply the 1/1000 figure by the inverse of the figure polled and you have an approximate ratio of people within the 14-22 age group who would attend kumoricon if they know about it to people who would not. Now, take that figure and divide it by 5. If that figure is greater than 1/1750 (twice the amount needed to break even) it's probably a good investment to make. If that figure is less than 1/3500, it's probably a really bad idea.