This page applies to pre-94 manual transmissions.  The synchros were redesigned in '94, and as far as I can tell they aren't problematic like the earlier synchros were.

Earlier Saab synchronizers (like many European manufacturers') won't take a lot of abuse.  The function of the synchronizer is to keep the gears from grinding when the transmission is shifted.  If a lot of fast, hard shifting is done, the 2nd and perhaps 3rd gear synchros will get weak, and the transmission will grind when shifting into these gears.  If it doesn't grind on normal shifts, try a fast up-shift just to see if it grinds; if not, then the odds are good that the transmission hasn't been abused.

The synchro rings only cost about $30, but the labor will probably be so much that you'd be better off installing a rebuilt transmission (from Eriksson).  Once a shop gets in there, there's no telling what they'll want to replace; it could get expensive in a hurry, as gear components are really steep.  The labor will eat you alive as well.  And you know what?  Most Saab dealers don't know their ass from a hole in the ground when it comes to rebuilding transmissions.  My local one sure didn't!  They typically put in a rebuilt when a car is brought to them with transmission problems.

If you remove the trans and take it to a shop, you might get burned as I did - they didn't get it back together quite right, and they wanted to wash their hands of it because they didn't remove it (and test drive it first).

Trying to do it yourself is really risky.  You can get around the special tools for the most part, but it's not easy, not pretty, and the chances of success aren't all that high.  Frankly, you just cannot beat an Eriksson rebuilt at $1500 or so.

The key to buying a used car is to find out if the synchros are in good shape, before you buy.  Lay a fast shift on 2nd and 3rd; whether it grinds or not, do NOT do it repeatedly; there's no point in abusing a bad one, and there's no point in abusing a good one either.  If it tends to grind, you'll have to decide whether you can live with it.  If you push a weak synchro repeatedly, it will just get worse.