Somebody asked me privately: “I just want to tell u that u have very nice collection of books.But wud like to know from where have u purchased this.I mean u purchased altogether or slowly slowly u gathered all books.Even i want to purchase so pls guide me from where have u purchased ? is it from library or second hand books .Pls let me know coz i cannot efford to buy all books together if they r costly.”
First–we do use our local libraries, and most sane people who read as much as we do simply make very frequent trips to the library. Since we can afford it, though, I prefer to own a lot of books. The great advantage of using the library (either because of not wanting to spend that money, or not having the money) is the great variety, and the child’s becoming familiar with the library…
Anyway, all that said, here are some notes on my book-buying strategy.
I did not buy them all at once, of course. I’ve made a trip to the bookstore (or order online) at least once a month for the last three years, though. Usually more than once a month, actually. I frequently plunk down between $50 and $100–or more–per visit. To save money, I have used Amazon and the local Half Price Books (used and overstock books) more lately. But I have become a Barnes & Nobel member and the member price ends up being only a little more than Amazon.
The advantages of a big (not small) new (not used or overstock) book store (not Amazon) are that you get to see and completely preview a very good selection of books before you buy them. The ones that tend to sell well, often do so for a good reason. It’s just more efficient, at least if you don’t already have a big book collection.
The big advantage of used and overstock bookstores is, of course, price. You can get the best prices (usually better than online, IMO) from these places. The disadvantage is that the book selection can frequently be idiosyncratic. But it’s really not that bad. If there’s a problem along those lines, it is that, if you go into a used book store looking for a particular volume, you won’t find it, unless you’re lucky enough to live near a really HUGE used book store. That’s the best of all possible worlds…
The great advantage of Amazon is that it has everything. If it’s in print, and often if it’s not, you can buy it at Amazon. (I don’t mention other online bookstores because I don’t use 'em…) The prices are also very cheap, especially if you go with the super saver shipping. Just remember that it’s generally $4 extra per book from any Amazon affiliate. Also, it’s of course really simple & saves gas money. 
It would be a big mistake to buy all the books you plan to buy over the next year in one giant shopping trip. You get an idea of what your child likes, then you buy more of that. You also might realize that you want a book on a certain subject, or more of a certain author. Buying smaller numbers of books more frequently gives you the freedom to tailor your reading that way.
The big thing I didn’t realize when I started buying children’s books was just what the variety of books are out there. I strongly recommend sampling different types of books. Not just picture storybooks and fairy tale collections, but sticker books, concept books, math storybooks (did you know they existed?), Berenstain Bears, the first of the “big” series (some, we’ve never tried), the many cheap “leveled readers” that teach science and history, the REAL children’s classics (most aren’t accessible to a child until age 2 or 3 at earliest) as opposed to the prize-winning ones which are frequently duds, the endless written-for-libraries-and-schools nonfiction books (sometimes they’re good!), “first encyclopedias” of this and that, other thick encyclopedia-type introductory books, the Oxford Picture Dictionary (a longtime favorite with my boy…regular reading for well over a year, and there are still many pages we haven’t seen yet)…it goes on and on. There is not just one type of book.
Hope this helps.