Its intriguing to see everyone in shock over the prices at Ashford Castle in September. You're missing the point. They have many rooms that don't cost $1000, but they have all been booked up by travellers (and coach tours) way in advance. Lets face it, September is only 3 months away.
If you want a good deal in an Irish castle, then Im afraid reserving 3 months in advance of arrival is too late to get it.
So all that is left now in Ashford Castle are junior staterooms which would be fit for a Saudi Prince or someone of that ilk.
As mentioned there are tons of other castles, that one just happens to be in the top 3, in my humble but expert opinion.
Incidentally, I got charged $540 for a non oceanview at the Fez Parker in Santa Barbara (sister city of Dingle) in September. Is it worth that? absolutely not. Would a junior stateroom in 12th century Ashford Castle be worth twice as much as a night overlooking the 1980's courtyard in the Santa Barbara Hotel? Absolutely.
Its all relative.
Rant over :)
Oh except, one other contributor made a good point. Don't be fooled by the marketing and spin which often sells you an Irish Castle experience, and then you arrive and find its a stately home from the late 1700's built in the Scottish baronial style. Thats not a castle! or at least not the type most Americans are yearning for. Go into Connemara and find a decent castle hotel, ideally 12th century, complete with murder hole above the front door and a dungeon. If it doesn't have a 'murder hole' then don't book!