You can setup different prices based on the number of members, but this must be done when creating the event the first time. If it's already there, you will not see the options to do this. So create a NEW event (or you can COPY what you already have and go from there)...
On the discounts & fees tab, you will see the place to provide the price for one person, which in this case is 293.75. Then you'll have 10 more pricing rows for groups. Set a price for 2 as 411.25 and 205.63 per person. Then for 3 people 528.75 and 176.25 per person. Then for 4 people... etc.
This is not exactly as you described, but the same end result. The way DT Reg calculates is always based on a per person rate. You can just change what the per person rate is based on the number of people in the group. Then just calculate that to get the final number that you need. Hope that helps.