Purchasing a Lizard

Question
My son desperately wants a lizard for his birthday.  He has been talking about it for months.  I am considering it, although in honesty, I am not thrilled with the idea.  I'm assuming a gecko would be best, but are there any that do not eat "live" things?  My ideal lizard would be small, clean, eat something not living and not live forever.  That may sound bad, but kids change their mind.  Speaking of changing their mind...what does one do with a lizard if you don't want it?  Do pet shops take them back?  Maybe Craigslist it--LOL!  Any advice would help!

Answer
Hi Beth,
You have asked some very important questions.  They are questions that, if more people asked, less people would most likely own lizards and less lizards would be abused, ignored, left for dead, let loose..etc...
Let me answer some of your ending questions first.
Most lizards have a long life span...15 to 20 plus years, including the leopard gecko and other gecko species. With many lizards, its not only the child getting bored, but it can be that child going off to college.
Sometimes, pet stores will take back a healthy reptile and sometimes you can sell them on craigs list and many rescues will take them, depending on species because of the space the species may need.
Here is a link to a very good article for parents of lizard wanting children. http://www.anapsid.org/parent.html
There are few herbivorous lizards...none of which are easy or inexpensive care.  Giant green iguanas require a huge cage(basically, a small room) live for 15-20+ years, have high upkeep with speciality lighting, require high temperatures(adding to the electric bill) and lots of other specialized care. Cheap to buy, expensive to keep.  Uromastyx are smaller than an iguana, but require even higher temperatures, but not as large of a cage.  Other species of iguanas fall in between the two above.
Leopard geckos are small(20 gallon tank), live for 20 years, are clean, may not be social, don't require special uvb lighting, require only one small area that is 88-92 degrees in their tank....but..eat only live foods...crickets, superworms, silkworms, etc.
Fat tailed geckos are basically the same care requirements as the leo. Crested geckos require a higher rather than long cage, but eat baby food fruits and insects...
An Anole, although not social in most cases, requires a 10 gallon tank, does need the special uvb lighting, does eat insects...but has a short life span...generally about 4 years.
Some of the skinks, such as the blue tongue skink eat both plant and insect, but require special uvb lighting, and also have a 20+ yr life span.  Temperature ranges are pretty much as the iguana for the most part.  Cage is a 50-75 gallon tank, depending on skink species.
Bearded dragons.... most are very social....eat both plant and insects, although as they get older, its more plant matter than insects... do require an area of a high daytime temperature, do require special uvb lighting...Don't generally have a long lifespan..maybe 6-10 years.
Depending on where you live, each species I mention have different costs to purchase.  In guessing, I would say anywhere from 10$ to possibly 100$ or more.
One other possibility, if your son is not going to give up on wanting a lizard, and you are willing to take on the expenses needed, etc...is to check into adopting an older lizard that is needing a home.
Thank you for all the wonderful questions!!!!