Hi,
It cost N25,750 for a students Visa to the UK. You may decide to pay at any of the avaliable VFS designated branches like the one on in Victoria Island on Ajose Adeogun ZENON House. It take between 15 to 20 working days for them to receive your application verify your claims as par bank statements blah blah blah and get a reply. If you want to make your payment at Zenon there is a GTB mini branch/ Service point that requires you to pay N250 just for the service. So in all you would spend N26,000.
I hope this is helpful. By the way what school are u looking at?
L8r

OBEXSUS