My advice to buy the visa yourself at the airport, do not get it from a travel rep as they often over charge. Queue up at the bank, if you have dollars hand over the exact amount. If you are paying in another currency like sterling or Euros make sure you are charged the exact equivalent, find out what $25 is before hand.
Egypt travel advice - GOV.UK: For visits of up to 30 days, you can get a visa on arrival by payment in Sterling, US Dollars or Euros. From 1 May 2014 the visa fee will be US$25. Alternatively you can get a visa from an Egyptian Consulate outside Egypt before you travel.