Walter R. wrote:
My house is 25 years old. When they built it, the builder put in toilets
that had an unusually deep recess for the wax ring and flange. All the
flanges in my house (5 toilets) stick out about 1/2" above the floor level.

Therefore, my replacement toilet (the old one was cracked), floats about
1/2" above the floor level, after allowing for the wax ring

The steel flange seems to be cemented to the plastic drain pipe. It would
cost a fortune to break
up the slab and the tile flooring, in order put in a new, lower flange.

Probably would not cost a fortune. You can cut off the flange from the
inside of the pipe with an internal cutter, and attach a new flange. I'd
be worried that the new flange might be too low, depending on how close
you can cut the old flange off.

Other than that, use a piece of 1/2" plywood, sealed with water seal,
cut a tad smaller than the outline of the toilet base, then sealed with
colored caulking the same color as the toilet, so the plywood doesn't
get wet when you wash the floor. No one would notice this if they didn't
know to look.

You could also use this product,
"http://www.quickfixplumbingproducts.com/prod03.htm", but in my opinion
this looks worse than going the plywood and caulking route. I once tried
to buy something from this company, but I could never find any way to
buy their products. They don't sell directly, and I could never find any
plumbing supply place that could get the products.