I know....it's such a hard thing to just "throw away" a basically new car seat, isn't it?? When our son (who IS my last child! :) ) outgrew his infant seat, we put it in a garage sale at a friend's house. As long as you are honest with people about the seat NOT having been in a wreck or otherwise damaged, and the "expiration date" (stamped on the underside of the seat) isn't close or past, then you should not have a problem with finding someone who can use it, but not necessarily afford a *new* seat.
The other thing you might be able to do is to call a local women's shelter, and see if they might be able to use it, or give it to one of their clients. Also, do you have any friends who are expecting, or might need a 2nd car seat for Grandma or the 2nd car?? You might also want to try calling the Salvation Army or CCA (in Lewisville). I know they help families replace items that have been lost in a fire or other disaster, and they might be able to help you find a new home for your car seat.
I'm so glad I'm not the only one that hates throwing "good" things away!!