My boyfriend is in England and he wants me to visit him there and he asked me to find out the cost of a visa.and he wants to know the exact price

Ok, you are really in Ghana, ( I traced your IP address) so many of these are dating scams which I know you are aware of. Almost 99.9999 percent of any email about a boyfriend or girlfriend in Ghana is a scam for money.

But you will first need a passport from your nation. Then a VISA

Here is the UK web site from their embassy, with address in Ghana to apply for the visa and the costs

UK Visa Information - Home Page