Cost is typically under $50 for everything; tiles, mastic, grout. 

New tub costsTub (fiberglass) $147 (HD)Watts pvc pop-drain kit $ 20 (HD)5 Sheets Hardi-backer $45 (HD)Box Backer-on screws $7 (HD)Fiber tape $4 (HD)12x12 wall tile $50 (HD)Non-Sanded Grout $15 (HD)Spray on Sealer $9 (HD)Tube Colored Caulk $7 (HD)Bag Speed Set $14 (HD)Bucket of Mastic $30 (HD)Tile labor $150Plumbing labor $50Add em up and thats what it costs.

These are put on like regular tiles (with mastic), then grouted. 

In such a context, it may not be expensive at all - we've had payback in as little as three years.To air seal ductwork - which is arguably more important than insulating - you can use appropriately rated ventilation tape (foil-based or other) or mastic.  

even if  removing the tiles,.you still have to level the floor and remove all the old mastic or grout.

You have to use cork mastic to glue down the cork and tile directly over it with multi-purpose thinset. 

Most are like the TV shows,,,installed on green dry wall with one sided 'mastic'. 

Use tile mortar, not a mastic or adhesive or "premixed mortar."

Old tile glued to floors with asbestos mastic is not a problem unless disturbed.

Mastic and thinset both age and lose elasticity over time, which is why tiles eventually start falling off walls on their own (i.e., nothing is forever).