I'd say stay away from the newer SAR-8's. The aluminum receiver really isn't very authentic looking, and seems to get beat up (even more) than the steel receivers due to the very energetic ejection of the brass this rifle is known for. Not to mention, Springfield is only able to do very limited repairs on them now due to lack of parts, as I found out after buying a problematic used one which I only ended owning for two weeks. The good thing is Springfield's warranty is excellent, and if they can't repair it, they will make it right. I got mine very cheap, but that was likely because it was problematic as mentioned above. I've seen them at gunshows for anywhere between $700-$950 depending on condition.
However, I've also seen the greek SAR-8's and imported FMP rifles (not kit rifles built on FMP receivers) for around $900-$1100 recently. These are sort of in a weird place, IMHO, as genuine HK 91's can still be had for as low as $1800 if you have a bit of patience. Since you're already dealing with a $1K+ firearm, I'd rather save the extra $700 and get the preban, real thing than a postban clone.
However, some of the older SAR-8's may actually be considered preban as well. One thing to look for is that the "8" was stamped on top of a "3". The pre-89 versions of these rifles were called SAR-3's, but the "transition" guns were restamped with an "8" upon the 89 import ban. However, for a period of time after the 89 import ban, it was perfectly legal to convert the rifle back into the original version with all the legal features. Springfield had a kit (I believe they called it an "accurizing" kit) that replaced the butthole stock with the original PG stock. 922(r) was passed sometime in 1990 and put a stop to this. However, if your gun was imported sometime between the actual 89 import ban and when 922(r) actually went into effect and was converted into what would be an unimportable configuration, it could be grandfathered as a preban.
Some that were just stamped SAR-8 would fall into this range as well, it is just the restamps are easier to pick out. If you are looking at a particular rifle and know the serial number, you can call Springfield and they'll tell you when it was imported. Typically, these guns will go for more $$$ than the postbans, but occasionally you'll come across someone who doesn't know what they have. Of course, in order for it to legallybe grandfathered, it did need to have those "evil" features readded prior to 922(r), which would suggest the owner does know that they have a preban. However, it would be difficult to prove one way or the other when this conversion actually took place, so if you do find one still in the butthole config that can be confirmed to have been imported between the original 89 import ban and 922(r), you'd probably be pretty safe in doing the conversion now and adding all the preban goodies you like, if you were so inclined...
Rocko