Who decides how much bond I have to come up with?
Only a judge can set bond amount: you appear before a judge to get bond, set bond or get bond reduced.
Because in all cases (except life felonies) you have the right to bond, the law requires you be brought before a magistrate within 24 hours. Most people have a bond hearing via a TV hookup from jail.
Bond hearings are held every day, seven days a week, 365 days a year.