Somebody on the other site reccommended this place:
the Holiday Inn South before...it's south of the city, right next to I-55. From there it's a short ride to downtown (LaClede's Landing nightlife, the arch, etc.) and then an easy hop back onto I-55 as you leave for SD (which keeps you out of city traffic and offers connections to all the major interstates that go through the area). I've never had any problems with my bike there and the entire property is isolated from other things around it, plus security makes rounds through the parking lot.
4234 BUTLER HILL ROAD
ST. LOUIS, MO 63129 UNITED STATES
Hotel Front Desk: 1-314-8940700 | Hotel Fax: 1-314-8940167
going to call them and maybe a few other places and see if they offer a group discount
should have 5-10 people for the night prior maybe not sure