Chief financial officers in the Midwest are increasingly optimistic about the economy, but they are wary of inflation, according to a survey by Grant Thornton LLP.    Fifty-seven percent of respondents said their companies plan to raise prices out of concern about increased costs for raw materials, according to the biannual survey. The figure increased from 37 percent six months ago and 27 percent one year ago, Grant Thornton said. Though hiring is tepid, 40 percent of chief financial officers said they plan to increase head count (up from 28 percent six months earlier), and 58 percent are optimistic about their own company’s financial prospects in the next six months (up from 48 percent).  The survey was conducted March 22 through April 6; it solicited opinions from 318 chief financial officers across the country.