I've been doing some research and it's hard to find a decent MBA program online with classes less than $1800. Here is the only one I know of:

Webster University - Webster University - $540/credit (online)
Each class at Webster is 3 credits and the MBA program is 36 credits (not counting prereqs)

Some schools offer reduced out-of-state tuition if you are affiliated with the military so that may help you as well.

Graduate school courses are overall much more expensive than undergraduate courses, especially if you want to take your classes online. There are a number of schools that offer great online MBA programs but you have to be willing to make the investment.