If you have a MacWarehouse catalog handy, they've almost always got a fold-out
section near the center that outlines what SIMM upgrades to buy for which
Macintosh models. As of this writing, memory is running about $50 per megabyte,
and aside from ordering the right speed and pin configuration, the biggest
issue has to do with how much you think you'll need to add. If you fill up
your computer with low-capacity SIMMs, then in order to expand again later
you'll be forced to remove the ones you already have and replace them with
bigger ones. We can go over all this in more detail if you'd like, or you
can just call a catalog company and have them explain the options to you.