If I recall correctly, there were some quality issues with the SA3. Sig used 2 manufacturers for their O/U's. The SA5 is supposed to be a very nice high quality gun. The SA3, to the best of my knowledge has been discontinued. I would check with Sig and make sure you can get firing pins and springs (I assume these have hammer springs) before I invested in one.
I'm not sure what your intended use is, but as long as I could get parts and the gun fit me well (have this checked by a smith) $800 is not a bad price for an O/U. You may want to look at used Browning and Beretta. I have seen B guns sell in very nice used condition for $800 to $1000.
Good Luck,
Giz
