If your M3 is a "pretty" camera, you could sell it on the bay and get back most of your money, maybe even make a profit. Contact well known resellers and locate a really nice M3 or M4 that has been recently CLA'd. Your money would be well spent and you would have peace of mind knowing that there were no hidden problems.
If you buy and sell repeatedly, you are doomed to never be satisfied with any camera that you purchase. I know, this is the way I worked my way into higher end SLR's (!!!). Now, I am rarely satisfied with the quality or condition of anything if it is not new.
Personally, I am saving for an M6 classic, and I plan on getting the MP finder upgrade. I have also budgeted for $250 in a CLA so that it will be "like new" on the inside.
What you feel right now for your M3 is akin to grief, you have discovered that your prize possession is mortal. IMHO, you should follow the advice of drewbarb and contact DAG about resilvering the mirror and getting a complete CLA. It will be worth the effort and cost, nothing is more satisfying than getting back a old friend rejuvinated and ready for another half century of real use. Don't make this M3 a shelf queen that you are ashamed of using.