how hard is it to get a bid from a decent house

Being that unconfident certainly won't help you, if the only houses you get bids from are "bottom tier" then that just means you click with those guys better and that's really all that matters. You'll find when you get to CU that people care about rankings during rush but after that it really doesn't matter.

The biggest mistake you can make during rush is pretending to be someone ur not. It might get you into a higher ranked house, but most of the time the fraternity drops you or you leave the fraternity because you end up not liking it. Rushing houses is like buying shoes: it could be the nicest, most beautiful, most popular shoe ever but your not gonna wear them for long if they don't fit or feel comfortable.