The National Institutes of Health (USA) which is the largest medical research organisation in the world is often representative of the levels of research funding in the west.
A concise list of funding vs disease is here:
Now most people when questioned, probably expect that in general, levels of funding will be proportional to economic costs, DALYs (Disability-life-adjusted-years - accounts for disability and early death).
Except that in a number of notable cases they aren't. HIV-AIDS for example received many times more funding than other diseases compared to the economic costs in the USA.
But that is not the real problem. There are a few diseases which are under-researched by a factor of 10-60 times when comparing the economic costs based on studies in the literature and the amount of NIH funding.
Example of such a study: http://care.diabetesjournals.org/con...3/596.abstract
edit - I would consider Diabetes to be on par in terms of funding, excluding HIV-AIDS which is off the charts... I was referring to different diseases when suggesting they are underfunded.
I wonder if you guys know (or are willing to find out) which diseases they are and for what reasons do you think they are under-funded?