Is a PUI registration fee category possible for conferences?

I'm really fortunate in how well my collaboration is going. We've had several conference abstract acceptances for my work and am hoping for more. Before the collaboration, I would go to 1-2 conferences per year, and the costs would generally fit within my institutional faculty development grant allotment, helped dramatically by the fact that one conference was in Chicago and had no registration fee, due to my AAPM membership. 

However, in this calendar year, I have attended one conference already and have three more to attend for the remainder of the year. And the costs are stacking up. Here's an outlay of the conference registration fees I will have for the year, even after taking advantage of early registration savings, one-day rates when I can swing it, etc.:

Conference 1: $815
Conference 2: $575
Conference 3: $695 (I'm sneaking in with the one-day rate, $340)
Conference 4: free (but I otherwise pay $447 for yearly membership, out of my personal funds)

Registration fees for conferences 1 and 2 are more than my faculty development grant fund amount from my college for the entire year. These costs listed above do not include airfare, hotel, and food. And they're lower than they could be, because I pay more than $1000 out of personal funds each year for professional society memberships. I have some remaining funds from my start up that I can draw from, but that won't last forever. My department chipped in to help with costs for Conference 1, but they of course can't do that for everything, and the other faculty members deserve any additional support we can give them as well. Another obvious place for getting funds is from fringe funds from grants, but I haven't yet been able to land an external one (although I'm feeing a teensy bit positive about my last application round).

In short, these costs are really tough for faculty from primarily undergraduate institutions! Travel costs, such as airfare or food aren't controllable from a faculty status perspective, but I wonder if conference fees could be.

A natural question is to wonder if I really do need to go to "all these" conferences. In my mind, yes. One focuses on imaging from a clinical perspective, one on the field of medical physics primarily from the view of physicists, a third is broadly about medical imaging, and the fourth is a biennial gathering focused solely on breast imaging. These are all elements of what it means to be involved in medical imaging.

 I know absolutely nothing about planning and executing conferences, but I wonder: is there a place for a middle tier of registration costs for faculty at PUIs, somewhere between trainee and full faculty cost? If you have experience planning conferences, especially large-scale mainstream science ones, I'd love to hear about the plausibility.