Hello,
you ring the us embassy & give them your details & passport number etc, they also take the non refundable charge for your visa during this phone call, which was last time we went $131, they take this from your card when you ring.. once you have done this, you will be sent an email & you need to scan in your acpo certificate which you will have to apply for from acro, this costs £35 or it did.. once you have done that & the embassy will notify you again, and ask you to ring to make an appointment.. you also have to scan in some other forms you complete, if you refer to my older posts you may find more info..
you used to have to complete the DS156, DS157 & VCU1 forms, they have now brought in another form, DS160, my husband hasnt used this one yet as it wasnt in when he had his last interview.. i think this replaces the DS156.. not sure though..
basically the cost of applying for your visa is the $131, £35 police cerificate & then you have to buy a photo for your applcation form.. your travel to london if thats where your going to apply, so noway near the higher price range you mentioned, which is good!!
if you search the us embassy website, it will tell you what you need when you ring, i would avoid ringing them unessicerily as it costs £1.20 per minute
the email they send to you once you have taken the first step gives you pretty much all the info you should need.. you should also take with you a few bank statements & maybe a copy of your mortgage or something, wage slips? as proof as ties to your country.. sometimes not asked for but better to ahve them to hand, they have looked at my husbands a few times.. hope this helps you..