Sounds like you don't want to gamble on a $350 engine, or a middle ground option for building the $350 engine. Id call these guys and price a crate engine.
http://www.coylechevybuickgmc.com/
This might be a little less than the dealer but if you have a problem, then what?
http://www.ebay.com/itm/CHEVROLET-IMPALA-MONTE-CARLO-VENTURE-ALERO-GRAND-AM-3-4-LITER-V6-ENGINE-2000-02-/271617452413?pt=Motors_Car_Truck_Parts_Accessories &hash=item3f3da9697d&vxp=mtr