Amazon claims 230,000 titles available for the Kindle. So you aren't going to find a good overview probably. It is well covered for newer books (I don't often find a new book that isn't available) and really old books. Mid-list titles are more problematic but part of it is that Amazon does not format the books but rather has to get them from publishers. So if a publisher doesn't want to be involved, they don't have to be. Amazon has a
Kindle section so you can browse there and see if the selection appeals to you.
As for pricing. Most mass market books are $9.99 or less (there are some technical books that cost more than $6,000 in Kindle format but that is still several hundred cheaper than the paper). And that price would be for books out only in hardcover (generally $24.99 list price). Books in paperback (around $7.99 list) are usually in about $4.99. Plus Amazon has about 3,000 free titles (mostly public domain but some publisher promotions) and most of the public domain electronic book sites offer the titles in Kindle readable formats (and conversion is easy if not).