Alright Mhunter!! Buicks Rock! I just sold my '70 GS 455 Stage One late last year to get... (you guessed it) my boat! I think I made the right choice!
Riv's are great cars. I love the '71 and '72 boat tails. In '73 the 5 MPH bumpers were added and that took away from the style of the rear end in my opinion. My dad bought a 72 Riv new, back when I was a kid. Guess that's where I got my love for 'em.
Riv's, like most Buicks, are very much a special interest car and worth whatever you can get. Find the right buyer and it may bring 10 - 12,000 grand if it is truly showroom. Want to sell it fast and it may be hard to get $5000.
A quick search on Classic Car Trader Online found '71's from $2500 to $9,950. I don't know if this link will work, but give it a try.
What color is it? Does it have the buckets and concole? I'd love to see some pictures. Hope you have great luck with it. Keep me posted! If I can help in any way, let me know.