It's not something that's commonly used really. Breeders may know more about it. That's quite a long journey for a hamster. But doable. I have picked a hamster up from 2 hours journey away before - either in the car with me or on the train. The downside I can see is there's no "personal" handover from one home to the next - ie from the previous owner to the new one. But maybe that doesn't really matter once the hamster has had a couple of weeks to settle. £100 is a lot - but then a trainfare that distance could cost that much too.
If the breeder is ok with it then it's a possibility - but I would only do it if it's a genuine breeder who is registered with the National Hamster Council.
This is the list of NHC breeders in the North
There is Amberhill Hamstery in Glasgow
Club Breeders – Northern Hamster Club
I would think as long as they are in a pet carrier and this is secured correctly - and presumably the breeder would ensure this and only use a suitable pet couriet - it is basically just a journey. But it would need to be just for the hamster - not other pets being transported at the same time - that would be too stressful for a hamster.
Ideally though, it would be better if you could visit and have a kind of "handover" of the hamster when collecting (or the breeder dropping off) as presumably it's a baby hamster. You're in Essex area aren't you? Reckon it would be more than 150 mile journey. It's about 200 miles from York to London. It would be best part of a day's journey probably - that's still doable as they do tend to sleep during the day.