I saw an ad on ebay that said a 110hp tdi on a  52 plate was only $125 per year road fund licence.

I bought a year for my 1999 90hp tdi and it was £220.

Are the very slightly newer 110hp ones that much cleaner, or is mine not right?

https://www.gov.uk/vehicle-tax-rate-tables

 

 

I assume your car is on the pre 2001 pricing. That seems absurd though, mine (110 bhp) is around the £125 mark per year. It is slightly cleaner if I'm correct due to the VNT turbo but not by /that/ much. 

I guess the VVT must make just enough difference then, hadnt thought of that.

Mine is pre-2001.

Had my renewal through the post yesterday, I wasn't surprised to notice it's gone up by another £5 - £200 a year now :(

90bhp also has a VNT turbo although i'm not 100% on the 1999 model, they may have been wastegated.

A 1999 car will be on the old capacity-based tax and not emissions based. Simples.