Building from used is a great option. If you want something ready to go, the cheapest is the express, the home defense version is available in a 7 shot matte finish piece. Can be had under $300. Just ordered one from Bud's, $266 plus shipping. Then I found out about a guy over on The High Road, selling same for $270 shipped! Downside here is no ghost ring or sights, just a bead. You'd have to add the ghost ring to meet your requirements (available from Trijicon for $99, plus someone needs to install them).
The same guy on The High Road (gotta look up his name, saw in another thread here) also has the Police Models. Most would say better than the Express (technically, it IS). Metal trigger group instead of plastic, stronger springs, better finish and smoother overall. SUBSTANTIALLY more money however. But available with Ghost Rings, and any other upgrades you want, including different stock configureations, sights, 8 rounds on a 20 inch barrel.
According to my local shop, (has both in stock) lots of guys are using the Express for three gun and doing fine.