Fan Assembly - 87161204930 WORCESTER 280 RSF
£68.74 +VAT + Carriage
http://www.boilersparesdirect.co.uk/
If it was me I would fit it myself (or at least attempt to) but all the boiler engineers will tut-tut and quote the Gas Safety (Installation & Use) Regulations 1998 and say tinkering without certification is a criminal act - although I have yet to see a report of a householder being prosecuted - but the boiler engineers are probably correct nevertheless.
The risks are likely minimal but the consequences of an error could be very severe.
A certificated Gas Safety chap should be able to do this in half an hour. He will be expected by virtue of his registration to undertake safety checks as well - this will cost more.
Good luck...
Peccavi, October 2009