Your profile doesn't mention where you are, but if you're close to Mexico or travel there, many glass shops down there can make you a new fitted mirror and some can make the convex mirror, all for just a few bucks.
I got two replacement mirrors from a drawing I made at a Mazatlan glass shop for under $12 USD. A taxi driver knew about the place. I did the install of one replacement mirror into the frame myself as the glass shop didn't do that, but it was fairly easy. (The other mirror was a spare, in case I hit another street sign on the freeway again).
The heater element was a sheet of heating wire attached to a sticky sheet that I carefully pealed off the smashed original mirror...it stuck right onto the back of the new mirror no problem. The new mirror I held in with a bead of silicone surrounding it on the edge. Not exactly like the original, but it worked.
No problem with it for several years afterwards either.
