The new chips rarely move at all. The pricing depends on where you have it done. Humane societies and established non-profit rescue groups actually get a lower price from the manufacturer for both the chips and registration than the price given to vets. If the animal is chipped by a humane society the registration will have to be sent in by them to get the lower rate. As part of their programs, both Avid and HomeAgain actually donate many readers to animal shelters. The modern readers will read all the common chips currently used.
The chips actually contain only an ID number. The numbers are coded to identify which manufacturer produced the chip. The person reading the chip then must call to get the information. (Keeping your information up to date with the registering organization is EXTREMELY important. From experience I can tell you it is terribly frustrating to find a microchip, only to call and get outdated information and so still be unable to contact the owner.)
I've inserted a lot of microchips for our local shelter. Even though it's a large needle the insertion site (between the shoulder blades) has little in the way of pain receptors and so the discomfort level on the animal is minimal.
From a personal perspective, I STRONGLY recommend these as a permanent form of identification. Tatoos can fade or be easily missed because they are covered by hair. Though we rarely saw an animal with a microchip, I've seen several stray animals come into our local shelter only to go home almost immediately thanks to their chip. I know of one person who's dog ran off at a rest stop while traveling - and they had him back within four hours because he was picked up by the local animal control, which found his microchip. This is clearly an extreme case, but it is a great example of the value of these chips.
We have 5 dogs and 8 cats - and rescue other animals (currently a mom cat and one remaining kitten are also living with us - her other two kittens have new homes.) Every one of ours is microchipped, including the rescues. Even though the cats don't go out, if a disaster should happen (tree falling on the house, etc.) we'd be able to locate our lost babies.