cheap/easy way to swap valve springs at home

I would just buy one, you will need it again.
I have one of each style listed below.

Here is a reasonable head off engine one.
http://www.summitracing.com/parts/kdt-383/overview/

And here is one that you can use with the head on the engine.
http://www.summitracing.com/parts/kdt-3271/overview/