Costs for SEPA in the UK currently vary by bank. First direct only charged me 4 GBP when I bought my Round5/5A order earlier this year.
http://www1.firstdirect.com/1/2/Foreignpayments The only wrinkle was that I had to phone them up to initiate the transfer. It can't yet be done from their website.
Citibank don't charge at all.
https://www.citibank.co.uk/personal/moving-money.do
According to
https://www.ecb.europa.eu/paym/retpaym/ ... ex.en.html SEPA must be fully implemented in UK (a non-euro area country) by 31 Oct 2016. It also says that "Payment service providers must apply equal charges to comparable cross-border and domestic payments in euro within the European Union (Regulation No 924/2009). This principle of equal charges has been reinforced by the end-date regulation (Regulation No 260/2012), which has eliminated the € 50,000 ceiling under which equal charges could previously only be applied."
While payments from one GBP account to another GBP account are fee free, it's not clear to me whether the above means EUR payments from a UK account to elsewhere within Europe will also have to be fee free after 31 Oct 2016.