Slow starting / Glowplug system?

My wife told me yesterday that her car has started to not start as fast as is used too. Last night when I took it to the store I noticed that the glow plug light didn't come on. Thinking this was a little odd, I opened the door and recyled the key. I didn't here the "click" that the GP relay normally makes. WHat are some other things to check out? The GP's are new as of last summer. So it shouldn't be that. If it is the GP relay, where is it, can i test it, and how much does a new one cost. Would a junk yard part be just as good as a new part?

Thanks fo the help.