I was haphazardly trying different dates (looking for a 2 week stay). It seems kind of random. Wednesday check-ins didn't seem to work, but the following day worked just fine. z5r promo code works to recieve a 25% discount on any length stay. So basically I got the Villa for 14 nights for 450UGX a night or about $3.50 for the stay.
I also checked the rates on Travelocity and can find no rhyme or reason for the differences posted. The 600UGX rate can be had for 305USD (without a prepayment or 100% cancelation policy), so what I had thought was a simple mis-posting of the currency involved, seems to be a bit more.
I tend to book these things pretty far in advance, so I'll have plenty of time to see how this works out, and I do have tentative plans to be in Uganda before arrival, if anyone needs shillings...........