CHRONIC unstable knee questions..plz HELP!!!?

i am a mom of 2 toddlers, & have a chronic unstable knee (possibly MCL damage) that limits me w/ any activities w/ kids. Unstable knee has "gone out" (severely)on me approx. 10 times, & will slightly "tweak" on me every other day. Now have constant pain, swelling, etc. Been through physical therapy twice with very little results., wear knee brace when absolutely needed . Dr wants MRI done to see what needs done with MCL or anything else during surgery. . My problem: NO INSURANCE!! MRI costs upwards of $600 i've heard, and i can't afford that, let alone surgery!!! has anyone had this kind of surgery? what is the approx. cost ??? any ideas of where i can get info on CHEAP insurance that will cover this, etc would be greatly appreciated!!! I so much want to be able to run & play with my kids!!!!!