I'm in a similar situation. I'm transitioning from a business-dress banking job (suit/tie, sportcoat/dress pant/tie) to a business casual corporate job.
Most of the people I saw during my office visits were wearing one of two outfits:
1. Cotton chinos (khaki, olive, navy, etc.) and a button-front sport shirt; or
2. Wool slacks (or chinos) and a polo-style/golf shirt.
I've chosen to dress one step better, dress pants and patterned dress shirts. Since I intend to lose some weight over the next few months, I didn't want to buy expensive shirts that won't fit (and would be too costly to alter) in a year; so, I shopped some discount stores (TJ Maxx, Marshalls, Syms) and low/mid-range department stores (Foleys and Dillards) for discounted shirts. I found several respectable options in the $15-30 range. I bought four new dress pants pants in the $100-150 range since they're much more easily (and affordably) altered.
As stated previously, Allen Edmonds are a good bet and can usually be found in the $100-150 range on sale. A step down the quality/price ladder would be Johnston & Murphy.