Here is the link from the stickies at the top...in MO, it looks like there are several places that base the fee on your income!http://www.lovethatcat.com/spayneuter.html#mo
Remember, you can either get them spayed, or keep them indoors only to prevent a pregnancy. I'm glad you have let your hubby know that you can't just trade one pet in on another due to gender. However, if you can't really afford to care for the current pets (including spay/neuter), I do not personally think you should consider keeping another kitten. In just a few short months, even the tiny newborns will be old enough to reproduce, and it is irresponsible to allow that.
Please check out the link, and start calling to check the possibility of spaying your kitties soon. Your last few weeks have been simply devastating, with the multiple deaths of babies from various causes. I cannot imagine you going through that horror again!