If your just doing the one repair, and are unlikely to do any others in the future then the MSW kit is probably reasonable value. If you bought the resin, hardener, glass matt and filler seperately you would probably be closer to £30. Thing is you would get 4x as much resin, way more matt and loads of filler, so per repair it would be way cheaper, but that assumes you keep needing to use it!
A comparible pack would be the West Systems Mini Pack, it contains similar items as the MSW kit, but around double the quantity of materials, if you search you can find it from around £10 to £15. You would still need to buy glass matt on top though, approx a £5er. This would give you a lot more materials for the money. Delivery on items like this can be quite expensive though due to the resin and hardener.
I've used East Coast Fiberglass Suplies a few times and their pricing is pretty good and quick delivery, west systems mini pack in link below, bear in mind thats exluding vat. http://www.ecfibreglasssupplies.co.uk/c ... fault.aspx
Other places such as http://www.cfsnet.co.uk/
or even http://www.axminster.co.uk/product-West ... 364830.htm
One of the best places to get this kind of stuff from in person is a local yacht chandlers, most will stock epoxy resin systems, fillers and fabric. They will most probably be slightly more expensive than buying online, but you don't have to pay delivery if you go in person.
Hope this helps, doesn't look like theres an easy answer unfortunatley!!!