I think Kmart and BigW have nice and cheap ones. I also bought every now and then from a special kids toy/book store. I loved Five Senses in Sydney ! https://www.fivesenseseducation.com.au/our-stores

If you want 2nd hand books you can try Vinnies or Salvos, otherwise borrow from libraries or by at bookshops

I was brought up on the kids Golden Books and you can find them in Kmart , Big W etc… It shouldn’t be too expensive but then it has been over 40 years since I read one .

i just get them from big w and they can be really cheap. depends on what you want

Ebay has a great range of baby books.
Big W, Kmart & Target have a good selection but Ebay offers more variety.
The wait can be a pain but I found I could get 2 books on Ebay for the price I would pay for 1 in Big W.

I find Big W have the best selection at good prices with some target stores having a good range (but slightly more expensive). You can also borrow from a library or bookdepository.com is located in the UK and often have books cheaper than here (and it only takes about 2 weeks for them to arrive).

I brought my kids’ books from discount book stores, Kmart & Big W, Some were cheap (they were the ones I let the kids chew and play with) and the more expensive ones we read together. I wouldn’t pay more than $5 for a board book that is going to be eaten lol

I just bought mine from the local book shop down the street, was around $20 if I recall but I was so excited I didn’t care about the price! If you are worried about cost maybe try the Facebook local buy sites to see if anyone is selling any secondhand?