How many free books have you read?
At least 200, a mix of classics (PG), indies, and other promos.
When deciding to read a free book, did you consider reading a book that cost money?
It depends on my mood. If I wanted to read, say, Jules Verne or some other classic , it's because that's what I wanted to read. It's doubtful I'd change my mind cause I'm an ornery sunnabitch, and reading something else in place of what I wanted would colour the experience of what I was reading.
However, if I was on an new author hunt then I would pick the book that most appealed to me whether it was free or not. I often use Dreams's excellent (but unfortunately not stickied) thread to find new authors . https://www.mobileread.com/forums/showthread.php?t=73900
Have you gotten a free book, and then decided to purchase a copy of the book? If so, why?
No, but I'll often buy more books by the same author if I liked a free one.
Has the availability of free books influenced your perception of how much a book should cost?
Why would it? IMO, a freebie book is just like any other coupon, BOGO offer, or giveaway by any other product manufacture. If I already like the product (author), I'm going to buy it anyway but it's nice to get it on sale. If I don't know the product(author), a good deal might entice me try it and to buy more.