I agree with all the others the particular car in question in grossly over priced. Also, the 87 to 89 cars are basically the same car. If you want you can always upgrade the rear wheels to 8’s and them move those 7’s on an 88 or 87 to the front which would arguably make it even more desirable then the 89. In all the usual internet sources there are always a reasonable crop of 87 to 89 carrera coupes. With some time spent working the internet you should be able to find some excellent examples.
A quick look at just eBay shows this one:
http://cgi.ebay.com/ebaymotors/1-OWNER-TEXAS-911-EXELLENT-CONDITION-75K-COLLECTOR-CAR_W0QQitemZ300232176826QQihZ020QQcategoryZ10156Q QssPageNameZWDVWQQrdZ1QQcmdZViewItem
I am not advocating that buy it now price or this car in particular but it took all of 30 second on eBay to find one much more reasonably priced.
Here is a 16k mile 87 cab for less then the offer of the one you’re looking at. I realize it’s a cab and you’re looking for a coupe but it’s just a data point.
http://cgi.ebay.com/ebaymotors/911-convertible-Only-16000-miles_W0QQitemZ120271807587QQihZ002QQcategoryZ1015 6QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
There are a couple of other 88 and 89 coupes and cabs on eBay which are much more realistically priced.
For my money, and I have bought and sold many many 911’s I would not even think of the car you posted anywhere near that price.
Auto Trader is also an excellent source with many many 87-89’s always listed. I generally won’t buy from a dealer because I trust my own buying skills and I don’t want to pay the premium that a deal needs to make. That being said as long as you’re not buying from a place like Victory who has a crappy reputation it’s not awful to buy from one of the handful or very reputable used 911 specialists out there.
Just my 2 cents, good luck. PM me if you have some specific questions, on my comments.