Organization-looking for the end all, be all software program

[Melissa Lohre]

I have a couple of small, multi-unit apartment rentals and some commercial spaces as well. I keep separate files on each of my properties but am finding I could use help with tracking rent payments and lease dates. My biggest issue right now is that I have okay'd a couple of tenants to make partial rent payments but I'm worried about tracking. Is there a software that anyone uses that would address this? I've looked at some (Buildium was one, I think) but feel that $40/month is more than I was looking to spend. I would be fine with a one time fee of sorts though. Any suggestions? Thanks!