I made the transfer on 26th Jan, using CHAPS, the cost was £25 fixed charge, that worked out at 0.05% as the amount was £48,000. The money was in the account in RP within a couple of hours.
The exchange rate was 69,175 (almost the interbank rate on the day)
Incidentally Nationwide messed up and delayed the transfer by a day. The rate fell slightly in that day (0.003). After complaining I got the refund for the lower rate (£144.50) plus £150 compensation.
Nationwide Debit card is still a reasonable way of drawing cash in RP I believe, even though they now charge £1 + 1%, but the rate is just about interbank.
If you have a better/cheaper way (with the interbank exchange rate) I would be pleased to know.
