1998 GMC Jimmy EGR Valve

I was told by a mechanic friend that the problem I am having is due to the EGR valve. He had used the scope and it read that the valve is the problem. It idles roughly - wants to stall bellow 2000rpm, but once it gets going it's fine. It's $250 to replace and I am concerned that if I replace it and the problem still exists, I won't be able to return the part - it may be something else. I did mget one from the wreckers but it did the same thing. If it is this, are there sites where prices are better? Thanks