I hear you on the flight prices - I just booked return flights to Little Rock, AR for 3 weeks' time and the fare was £550 (£200 for the ticket, plus £350 in taxes!). AA was cheaper from Manchester though (£521) but the plane was smaller and older and wouldn't have had screens on the seats or anything.
One-way flights have always been generally more expensive than return tickets. Usually because in general return tickets are more popular and can be offered cheaper. Also, I think a lot of one-way travellers are business people and their companies pay the fares, so there isn't so much competition for fares.
Sometimes you get lucky and find a cheaper one-way, but in general, it's cheaper just to book the return flight and then either not use the second ticket or book it for a later date, when you want to go back for a visit.