Suggest me good places to get used fiction/engineering books at very less price.

I already searched on google and reddit found few recommendation like moore market. But their used books are also expensive. Found one more siva house but seems like this place no longer exist. So asking for advice here.

So I want to know bookstores where I can get very cheap used/unused books.

I want some fiction/non fictions based on availability and some computer science books.

I live in Velachery. So nearby it would be better but distant stores are also fine if I am getting books in good price

Thanks.