Kathy, buy a used version of Aperture on E-bay.

Apple's licensing agreement specifically allows a one time transfer and you even get to register the used software in your own name even though previously registered. This entitles you to auto-updates too.

I know this as I sold some of my Apple software and I called Apple customer service and they showed me right in the software licensing agreement where it authorizes a one time transfer.

Just make sure you do not buy the academic or non-retail version.