Is there anything I can do to get by with my expired tags?

My wife worked for Chrysler and was laid off during all that jazz a few years ago. We both had "company vehicles" and had to turn them in. We both had to buy new vehicles and we were in no position to do so. We tried to find alternatives but we only had the credit/cash to buy brand new vehicles (love how that works, no money = new car instead of old one) so we did what we had to do or else we were walking home. To get the deal done, they had to roll the money the bank gave us for taxes and tags into the down payment. So about 3 years later now we still don't have the 4k in sales tax and personal property tax. We have the old tags from my wifes first vehicle thrown on her new car but they're expired. We did the same with mine but since I once owned a car and now own a truck the tags didn't match so a cop confiscated them when he pulled me over. So now we share her car because mine has no tags and could get confiscated by a cop with nothing better to do. And her car has her old expired tags on them and we're hit with tickets every other week if not more. We don't have the 3k and every time we get close something comes up and we need it elsewhere. We've gotten by paying the tickets but it's cost us perhaps a thousand bucks over the last two years. There has to be something we can do. We live in Missouri if that matters. HELP!.