There are a lot of options for you here in Missouri. As stated before you have to go through a P.O.S.T. approved training facility to work as a Police Officer/Sheriff's Deputy/Highway Patrolman, in Missouri. Most agencies outside of Stl, Sprgfld, and Kc only require 480 hour class B certification. However, 800 and in some cases 1000 hours are becoming the norm.
As said before, If you can get a large department to hire you, say St. Louis County Police, then they pay for you to go through there academy, pay you while you are in the academy, and furnish you with all of your gear. The catch is you have to work for there deaprtment for at least one year after completion of the academy, or you must pay back you tution cost.
There is the Missouri Police Corps., they pay your way as well, but the catch is you must stay with the first department you start at for 4 years, and make yourself available for their purposes for that time period, meaing they can call you on your day off and ask you to put on a class at a highschool, and you don't get paid for it.
The third option is to attend a regular academy. There are some that will get you through in as little as 6 months, those are M-F 9to5 facilities, making it almost impossible for you to hold a job while attending. I attended a 800 hour course that took me a year and 9 months to complete. We met three days a week for 4 hours a night/day, they beauty of it was they offered the same class twice in one day, so you could either attended the morning class, or the evening class depending upon what your work schedule allowed.
If you have a place to stay, i.e. parents house, and you have the G.I bill, I recommend getting it done quickly with a full time academy.
Last but not least, plan on getting at least an Associates Degree, the days of High School being "good enough" are long gone. Most of your higher paying departments require a Bachelors degree.
Good Luck.
Edited to add: Here is a list of POST approved facilities in MO.
www.dps.state.mo.us/dps/dps2002/POST/LicensedBasicTrgCenters.htm