Yes, this is an ancient thread. But for the next guy searching...
Beaver made a bunch of different saws before being bought out by Rockwell, who then merged with delta.
Things to look for:
1. Cast iron top. Sheet metal tops bend, flex, dent, and are a PITA. Tolerable for construction sites where 1/8" is good enough.
2. extension wings on either side. Allows you to handle wider work -- and to have a bigger table to accumlated junk.
3. Body: Heavy gauge sheet metal at least. Some have a partial cast body.
4. Drive train: Check for play in the whole saw support mechanism. Bearings in the blade shaft are easy to replace. Check the rack (tilt and rise) castings for cracks. Those are show stoppers as very hard to replace.
5. Fence. Move easily? Ok. Slide it over to to one of the mitre slots. Clamp it. Is it perfectly parallel to the slot. Try clamping while putting a bit of sideways pressure on the far end. An inconsistent fence isn't a show stopper, but it will either require work or replacement. Usually it's designed in so you need a replacement.
So, what is it worth: Easiest way to find out the value is to look at ebay and search for closed listings. This will tell you what others like it sold for.
Here, in Edmonton good beavers go for 100 to 200 bucks.