I got that sent to me too could quite believe it as I only paid $8.99 for a .com address from registerfly.com and they sent to me saying it would be £80 + VAT
this is the reply when I questioned them,
"Thank you for your email. The domain name was invoiced to your at the
full rate of £80 + VAT because the service provider attached to your
domain name had not indicated that they were renewing the domain name on
your behalf. The discounted rate for renewals only applies if the service
providers renew the domain names on behalf of their registrants as they
received a discounted rate."
I think they are perhaps some sort of scam using the nominet name as well no one would pay that for a domain name, I'll just get the name again from registerfly for $8.99, it sounds iffy to me.
I don't even use the domain name in question anymore but have a few more up for renewal soon, wonder if I'll recieve the same email.