Help with Speakers

My Husband has a 1993 GMC Sierra C1500 - he has orig. stereo. Want to get him CD player and speakers for his B'day. His parents are going to handle the CD but I want to get him new speakers. I mean music coming from the factory speakers hurts my ears. Anyway I call myself searching the Internet for the speaker size needed? From what I can tell so far I have to get the same size speaker that is already in there??
BDAY is July 12th
SO my questions are #1 What size are the factory installed speakers? #2 Any recommendations on type of speaker to get to replace the ones he has? Trying to make this a surprise. Do I have to get the same size? Don't want anything that is booming or expensive, you know just decent conservative speakers. I am talking like $100 or less for new decent speakers, is this reasonable for good speakers?

Help, as you can tell I know nothing :)
Thanks, I am sure he will appreciate that I found this site when it comes time to work on the truck again.

the best fir for that model is a 4 X 6 in the dash and rear piller if xtemded cab.
you can check cruchfield or sounddomain on the web
or check at local store try to get speakers with an wattage rating the same or higher than the cd reciever try to get a good 3 way speaker
you can get a really good set for 100 but most are cheeper
there are a lot of good brands clarian, alpine, panasonic, ect..