I bought Groo off the stands as a kid and held them until the mid-90's when I sold off a large chunk of my collection. I don't remember any of them being worth anything except the issues Shadroch noted (the independent series/appearances and 1st Marvel issue). $20-30 back in the late 80's would have been a very significant amount of money for a modern book.
Actually, let me just get off my duff and grab a CVM.
Here's July 1989 listings for Groo....
As a point of reference, the Punisher Limited Series was $22 in this issue and the Wolverine Limited was $18 GI Joe #2 was $35 and Groo #1 (Marvel) was $15, so the $20-30 range is really out of the question for this book during that period. I jumped up a couple of years to an Overstreet Monthly from 1991 and this issue isn't even broken out. Maaaayyyybeeeee a few years after and just before the crash, but it doesn't really stand out as anything significant in my mind and I tried to stay up on any hot books through that period. I feel like Wizard would've had to really be hyping this issue to get that large an asking price, but maybe someone else has a different recollection.