Ah, see here in Southampton, we have a 12 week Nuchal scan (to test for downs) and a 20 week anomoly scan.
You can get more scans, but only if there is a medical reason (my friend had regular scans because she has kidney disease)
It is completely up to the hospital how much they charge for pics (it is after all, a medical test to test for abnormalities - not a test to find out gender or for the parents to see baby)
I was lucky, in that my hospital will tell you what they think the gender is if you ask them. Some hospitals will refuse to even look in case someone sues them if they get it wrong!!!