As well as the 'type' of ad, it would also depend on placement. Pbooks, especially paperbacks, have long had ads-usually at the very back of the book, and almost always for other books.
I like the idea of consumer choice-I'd probably try the 'with-ads' version for the lower price, as long as I didn't find the ads objectionable. If I did, then I'd pay for the 'without-ads' version in the future. (Or maybe even for another copy of the same book if I found them *that* objectionable, and thought the book was good enough to justify re-purchasing it.)
Basically, I don't fear ads. The only reason for objecting to them, IMO, is when they 'get in your way'. (Ads placed in the middle of a pbook do, IMO, get in the way. Ads placed at the beginning or end, IMO, don't.)