My first thoughts as well.
But the OP might not be testing any network performance issues, and just need seperate broadcast domains.
In any event, this set of requirements doesn't seem to include "fast", nor does it include "switch" (as opposed to router). To me, "layer 3 switch" means "IP forwarding with an ASIC". I think that's a pretty common interpretation.
I'd solve this problem with a PC (those are free, aren't they? :-) with4 NICs (also free).