Sedalia has free parking at their newly renovated station. Very nice perk, considering we have to drive a little over 2 hours to get there. Jefferson City, our next-closest station, has no free overnight parking (one can park for free on weekends/holidays on the metered spots along Jefferson St., which is the street that one sees from the River Runner), but a monthly pass can be obtained (prices vary by lot, but tend to be about $30/mo; the city owns several, and several are for-profit lots).
When Springfield gets a train station, I expect we will need to pay to park. First of all, the location favoured by the city (to any who might be familiar with the city, it's at Commercial St. & Washington Ave., the site of the ex-Frisco station now used by BNSF for freight, but would be a new construction next door) has only one off-street lot nearby, and although on-street parking is plentiful along Commercial St., it is not intended for overnight parking. Fortunately, that area also has some of the best bus service in Springfield, but the lack of any regional bus service or park-and-ride facilities means those of us out in the suburbs will still need to drive downtown. Springfield-Branson airport (SGF) charges $8-15/day, depending on the lot, so I expect that parking fees would not be any higher than that, and probably substantially lower.