John,
You can download the program and use it for 30 days as a trial then buy a license. There is no difference between the trial and paid versions, just a serial.
I suggest just download and install on each computer. The file is available online 24-7 on Adobe's site.
You can purchase a serial from the Adobe Store at any time, they will email it to you. This I printer out to save even though my account with Adobe lists all my software and serial numbers back to CS2 and LR1.
Just some of the options open to you.
Rich
P.S. Just before I came over to the form I processed a photo of my grandson playing in the pool. The photo was so blown out I have not been able to save it and others no matter what I tried (C!,NX2,LR3, RawTherapee, ACR6). With LR4 I have a usable photo.