When you say 'cost' are you referring solely to the Avios required? If so, then most of the North Eastern US cities (as far as ORD) require 20k for direct 1-way flights. Charges on top of that for BA flights are much the same for those destinations. The BOS-DUB on EI are 12.5k for the DIRECT service but charges will be a fair bit lower than BA.

As someone has pointed out, using BA to DUB requires a connection so you'll need more Avios.

I would also add AB from JFK to TXL to the list. It requires 20k Avios and just £1.60. I don't know how much the charges on the EI BOS-DUB are but they can't be much less than that.