Marina wrote:
My sister says she needs a special air filter for her Trane furnace/air
conditioner.
(that's all the info I got from her).

The technician came out to measure for a filter today and said it would
cost $700. She needs extra filtering due to asthma and lots of dust in her
house.

I'm hoping there is a good site where the cost is a little lower and you
know they are a good honest site?
Thanks.
Marina

If this is making a new filter housing for the unit I would try to find
out the actual filter cost and the materials and labor breakdown. $700
may be ok at the rates some places charge.

In my previous house I used to run an electronic air cleaner on the
central air system . More expensive to install but cheaper to operate
long term.