Certainly, Jack could afford a price tag of $240,000, or possibly even more; she's the money behind Keeley's PR firm and has made several conspicuous comments about her massive wealth. That's not the point, though — tracking down an Austen first edition would probably take months, it wouldn't be contained in one book, and it's nearly impossible to find a signed copy, if not outright impossible.
Within the narrative, though, this is used as an example of Jack potentially "love bombing" Keeley — that is, showering her with affection and presents too early in the relationship with the idea that she might suddenly withdraw later. Keeley only even thinks of this when Rebecca (Hannah Waddingham) brings it up as a possibility while the two are out at dinner... a dinner secretly paid for in full by Jack, despite not even being present. Luckily, Rebecca's warnings, which she gives Keeley with the best of intentions — after experiencing love bombing with her awful ex-husband Rupert (Anthony Head) — don't come to anything bad, as Jack was simply trying to be generous with Keeley. After that, all is resolved when Keeley takes Jack out to a restaurant of her choosing... and even gives back Jack's latest extravagant gift.
