There's a lot more that ought to motivate someone for any job, especially when that job is holding public office. People are motivated by pride in their work, civic duty, a sense of purpose, and dozens of other "intangibles". Take a look at all the staffers working for this guy on Capitol Hill (very few make more than $40K despite being among the best and brightest young people in the country). Right now, I've got friends graduating MIT and entering the Peace Corps, and I took at $30,000 pay cut to move from one engineering job to another because I wanted to work on something I'd be proud of.
If you want quality talent, and people more difficult to bribe/influence, you MUST pay them well.
Anyone whose susceptibility to bribery changes with their salary is already unfit for public office. What you pay is not the only factor in any job. Do you really want a crop of candidates who are "in it for the money"?