Registry wedding/registrar

Hi all!
Now this might be a silly question, but my other half and I have wanted to get married for a while and this evening I have been researching all about how to go about it. Neither of us is religious and we don’t want a big hotel wedding either, we both agree we’d like a small intimate wedding at a registry office and maybe a party at home later or for our 1 year anniversary.
My question is: other than our two witnesses, does anyone have to be at the registry office when we get married? What is the point in a registrar, do we have to have one and why are they so bloody expensive 😂 I really just want a no fuss, no frills ceremony with just my other half and obviously whoever else *has* to be there. If anyone could help me out that would be so great! The info online is more than a little bit confusing lol. Thanks guys!