I have purchased a few fogless mirrors to shave in the shower and this one has come out the best. It's a little more expensive than others, but the design is what you are paying for. Most fogless mirrors have chemical coats that degrade fairly quickly, but by adding the tank they use heat (warm water) to overcome this issue. Usual OXO high quality, just make sure you clean the surface before applying the suction cup.
Product was last $27 in May 23 according to 3xcamels
Mirror glass size 18.5cm x 12.5cm (I just measured it, not sure what 3" is about)
I'd love this but I think $27 is a stretch