Take 2 yen off today's official exchange rate and that's the exchange rate I'll give you.
I'll give you whatever today's rate is minus 2 yen for fees.
「当日のレートから手数料2円を引いたレートで両替してあげる」= Take 2 yen off today's official exchange rate and that's the exchange rate I'll give you. / I'll give you whatever today's rate is minus 2 yen for fees.
ボキャブラリー
take(~off), minus = 引く
today's = 今日の・本日の
(official) exchange rate = (公式の)レート
that's = それは、それが
give you = あげる
fees = 手数料